diff --git a/icu4c/source/common/propsvec.c b/icu4c/source/common/propsvec.c
index d3ece4eab05..41e8b9bbf73 100644
--- a/icu4c/source/common/propsvec.c
+++ b/icu4c/source/common/propsvec.c
@@ -276,11 +276,13 @@ upvec_setValue(UPropsVectors *pv,
 U_CAPI uint32_t U_EXPORT2
 upvec_getValue(const UPropsVectors *pv, UChar32 c, int32_t column) {
     uint32_t *row;
+    UPropsVectors *ncpv;
 
     if(pv->isCompacted || c<0 || c>UPVEC_MAX_CP || column<0 || column>=(pv->columns-2)) {
         return 0;
     }
-    row=_findRow((UPropsVectors *)pv, c);
+    ncpv=(UPropsVectors *)pv;
+    row=_findRow(ncpv, c);
     return row[2+column];
 }
 
diff --git a/icu4c/source/common/uhash.c b/icu4c/source/common/uhash.c
index f3ffd0497ba..0018167d05f 100644
--- a/icu4c/source/common/uhash.c
+++ b/icu4c/source/common/uhash.c
@@ -798,7 +798,8 @@ uhash_removeElement(UHashtable *hash, const UHashElement* e) {
     U_ASSERT(hash != NULL);
     U_ASSERT(e != NULL);
     if (!IS_EMPTY_OR_DELETED(e->hashcode)) {
-        return _uhash_internalRemoveElement(hash, (UHashElement*) e).pointer;
+        UHashElement *nce = (UHashElement *)e;
+        return _uhash_internalRemoveElement(hash, nce).pointer;
     }
     return NULL;
 }
diff --git a/icu4c/source/i18n/repattrn.cpp b/icu4c/source/i18n/repattrn.cpp
index bd4518cfe1e..bfe2520ad61 100644
--- a/icu4c/source/i18n/repattrn.cpp
+++ b/icu4c/source/i18n/repattrn.cpp
@@ -29,8 +29,6 @@ U_NAMESPACE_BEGIN
 //
 //--------------------------------------------------------------------------
 RegexPattern::RegexPattern() {
-    UErrorCode status = U_ZERO_ERROR;
-
     // Init all of this instance's data.
     init();
 
diff --git a/icu4c/source/i18n/tmutfmt.cpp b/icu4c/source/i18n/tmutfmt.cpp
index 1576f69d92c..94e97e1fc84 100644
--- a/icu4c/source/i18n/tmutfmt.cpp
+++ b/icu4c/source/i18n/tmutfmt.cpp
@@ -800,12 +800,12 @@ U_CDECL_BEGIN
  * @param val2  the other value in comparison
  * @return      TRUE if 2 values are the same, FALSE otherwise
  */
-static UBool U_CALLCONV hashTableValueComparator(UHashTok val1, UHashTok val2);
+UBool U_CALLCONV tmutfmtHashTableValueComparator(UHashTok val1, UHashTok val2);
 
 U_CDECL_END
 
 UBool 
-U_CALLCONV hashTableValueComparator(UHashTok val1, UHashTok val2) {
+U_CALLCONV tmutfmtHashTableValueComparator(UHashTok val1, UHashTok val2) {
     const MessageFormat** pattern1 = (const MessageFormat**)val1.pointer;
     const MessageFormat** pattern2 = (const MessageFormat**)val2.pointer;
     return *pattern1[0] == *pattern2[0] && *pattern1[1] == *pattern2[1];
@@ -822,7 +822,7 @@ TimeUnitFormat::initHash(UErrorCode& status) {
         status = U_MEMORY_ALLOCATION_ERROR;
         return NULL;
     }
-    hTable->setValueCompartor(hashTableValueComparator);
+    hTable->setValueCompartor(tmutfmtHashTableValueComparator);
     return hTable;
 }
 
diff --git a/icu4c/source/i18n/unicode/tmutfmt.h b/icu4c/source/i18n/unicode/tmutfmt.h
index 85b4795a43c..aa076aff907 100644
--- a/icu4c/source/i18n/unicode/tmutfmt.h
+++ b/icu4c/source/i18n/unicode/tmutfmt.h
@@ -1,6 +1,6 @@
 /*
  *******************************************************************************
- * Copyright (C) 2008, Google, International Business Machines Corporation and *
+ * Copyright (C) 2009, Google, International Business Machines Corporation and *
  * others. All Rights Reserved.                                                *
  *******************************************************************************
  */
@@ -38,7 +38,7 @@ U_CDECL_BEGIN
 /**
  * @internal ICU 4.2
  */
-static UBool U_CALLCONV hashTableValueComparator(UHashTok val1, UHashTok val2) ;
+UBool U_CALLCONV tmutfmtHashTableValueComparator(UHashTok val1, UHashTok val2) ;
 
 U_CDECL_END
 
@@ -228,7 +228,7 @@ private:
     PluralRules*  fPluralRules;
     EStyle           fStyle;
 
-    friend UBool U_CALLCONV hashTableValueComparator(UHashTok val1, UHashTok val2);
+    friend UBool U_CALLCONV tmutfmtHashTableValueComparator(UHashTok val1, UHashTok val2);
     
     void create(const Locale& locale, EStyle style, UErrorCode& status);
 
diff --git a/icu4c/source/test/cintltst/callcoll.c b/icu4c/source/test/cintltst/callcoll.c
index f37fa804c9f..36068b521af 100644
--- a/icu4c/source/test/cintltst/callcoll.c
+++ b/icu4c/source/test/cintltst/callcoll.c
@@ -503,7 +503,10 @@ backAndForth(UCollationElements *iter)
 
     /* synwee : changed */
     while ((o = ucol_previous(iter, &status)) != UCOL_NULLORDER) {
-      int32_t offset = ucol_getOffset(iter);
+#if TEST_OFFSETS
+      int32_t offset = 
+#endif
+        ucol_getOffset(iter);
 
       index -= 1;
       if (o != orders[index].order) {
diff --git a/icu4c/source/test/cintltst/chashtst.c b/icu4c/source/test/cintltst/chashtst.c
index c70ae2bca5d..ae83f5b10b1 100644
--- a/icu4c/source/test/cintltst/chashtst.c
+++ b/icu4c/source/test/cintltst/chashtst.c
@@ -1,6 +1,6 @@
 /*
 *******************************************************************************
-*   Copyright (C) 2000-2005, International Business Machines
+*   Copyright (C) 2000-2009, International Business Machines
 *   Corporation and others.  All Rights Reserved.
 *******************************************************************************
 *   Date        Name        Description
@@ -47,26 +47,26 @@ void addHashtableTest(TestNode** root);
  *********************************************************************/
 
 static UBool
-_compareChars(void* a, void* b) {
+_compareChars(const void* a, const void* b) {
     UHashTok s, t;
-    s.pointer = a;
-    t.pointer = b;
+    s.pointer = (void *)a;
+    t.pointer = (void *)b;
     return uhash_compareChars(s, t);
 }
 
 static UBool
-_compareIChars(void* a, void* b) {
+_compareIChars(const void* a, const void* b) {
     UHashTok s, t;
-    s.pointer = a;
-    t.pointer = b;
+    s.pointer = (void *)a;
+    t.pointer = (void *)b;
     return uhash_compareIChars(s, t);
 }
 
 static UBool
-_compareUChars(void* a, void* b) {
+_compareUChars(const void* a, const void* b) {
     UHashTok s, t;
-    s.pointer = a;
-    t.pointer = b;
+    s.pointer = (void *)a;
+    t.pointer = (void *)b;
     return uhash_compareUChars(s, t);
 }
 
diff --git a/icu4c/source/test/cintltst/cloctst.c b/icu4c/source/test/cintltst/cloctst.c
index 4e0a860c886..69f8effe48c 100644
--- a/icu4c/source/test/cintltst/cloctst.c
+++ b/icu4c/source/test/cintltst/cloctst.c
@@ -2605,7 +2605,7 @@ typedef struct OrientationStructTag {
     ULayoutType line;
 } OrientationStruct;
 
-const char* ULayoutTypeToString(ULayoutType type)
+static const char* ULayoutTypeToString(ULayoutType type)
 {
     switch(type)
     {
@@ -5205,7 +5205,7 @@ static void TestLikelySubtags()
         const char* const minimal = basic_maximize_data[i][0];
         const char* const maximal = basic_maximize_data[i][1];
 
-        const int32_t length =
+        /* const int32_t length = */
             uloc_addLikelySubtags(
                 minimal,
                 buffer,
@@ -5231,7 +5231,7 @@ static void TestLikelySubtags()
         const char* const maximal = basic_minimize_data[i][0];
         const char* const minimal = basic_minimize_data[i][1];
 
-        const int32_t length =
+        /* const int32_t length = */
             uloc_minimizeSubtags(
                 maximal,
                 buffer,
@@ -5258,7 +5258,7 @@ static void TestLikelySubtags()
         const char* const minimal = full_data[i][0];
         const char* const maximal = full_data[i][1];
 
-        const int32_t length =
+        /* const int32_t length = */
             uloc_addLikelySubtags(
                 minimal,
                 buffer,
@@ -5286,7 +5286,7 @@ static void TestLikelySubtags()
 
         if (strlen(maximal) > 0) {
 
-            const int32_t length =
+            /* const int32_t length = */
                 uloc_minimizeSubtags(
                     maximal,
                     buffer,
diff --git a/icu4c/source/test/cintltst/creststn.c b/icu4c/source/test/cintltst/creststn.c
index ba95321204b..9dcef6e2153 100644
--- a/icu4c/source/test/cintltst/creststn.c
+++ b/icu4c/source/test/cintltst/creststn.c
@@ -37,8 +37,6 @@
 static int32_t pass;
 static int32_t fail;
 
-static void TestCLDRVersion();
-
 
 /*****************************************************************************/
 /**
@@ -182,6 +180,7 @@ static void TestGetFunctionalEquivalent(void);
 static void TestCLDRStyleAliases(void);
 static void TestFallbackCodes(void);
 static void TestGetUTF8String(void);
+static void TestCLDRVersion(void);
 
 /***************************************************************************************/
 
@@ -2956,7 +2955,7 @@ TestGetUTF8String() {
     ures_close(res);
 }
 
-void TestCLDRVersion() {
+static void TestCLDRVersion(void) {
   UVersionInfo zeroVersion;
   UVersionInfo testExpect;
   UVersionInfo testCurrent;
@@ -2983,9 +2982,6 @@ void TestCLDRVersion() {
   {
     UResourceBundle *res;
     const char *testdatapath;
-    char buffer8[16];
-    const char *s8;
-    int32_t length8;
 
     status = U_ZERO_ERROR;
     testdatapath = loadTestData(&status);
diff --git a/icu4c/source/test/cintltst/spooftest.c b/icu4c/source/test/cintltst/spooftest.c
index d8e96bd3cf1..c7c839ec28a 100644
--- a/icu4c/source/test/cintltst/spooftest.c
+++ b/icu4c/source/test/cintltst/spooftest.c
@@ -63,29 +63,6 @@ log_err("Test Failure at file %s, line %d: \"%s\" is false.\n", __FILE__, __LINE
 }
 
 
-static void test_assert_string(const char *expected, const UChar *actual, UBool nulTerm, const char *file, int line) {
-     char     buf_inside_macro[120];
-     int32_t  len = (int32_t)strlen(expected);
-     UBool    success;
-     if (nulTerm) {
-         u_austrncpy(buf_inside_macro, (actual), len+1);
-         buf_inside_macro[len+2] = 0;
-         success = (strcmp((expected), buf_inside_macro) == 0);
-     } else {
-         u_austrncpy(buf_inside_macro, (actual), len);
-         buf_inside_macro[len+1] = 0;
-         success = (strncmp((expected), buf_inside_macro, len) == 0);
-     }
-     if (success == FALSE) {
-         log_err("Failure at file %s, line %d, expected \"%s\", got \"%s\"\n",
-             file, line, (expected), buf_inside_macro);
-     }
-}
-
-#define TEST_ASSERT_STRING(expected, actual, nulTerm) test_assert_string(expected, actual, nulTerm, __FILE__, __LINE__)
-
-
-
 static void TestUSpoofCAPI(void);
 
 void addUSpoofTest(TestNode** root);
diff --git a/icu4c/source/test/cintltst/spreptst.c b/icu4c/source/test/cintltst/spreptst.c
index ed7ccbf294a..f0d18581929 100644
--- a/icu4c/source/test/cintltst/spreptst.c
+++ b/icu4c/source/test/cintltst/spreptst.c
@@ -751,7 +751,7 @@ UStringPrepProfileType getTypeFromProfileName(const char* profileName) {
 }
 static void TestStringPrepProfiles(void) {
     UErrorCode status = U_ZERO_ERROR;
-    char *profileName;
+    const char *profileName = NULL;
     UChar src[SPREP_PROFILE_TEST_MAX_LENGTH];
     UChar expected[SPREP_PROFILE_TEST_MAX_LENGTH];
     UChar result[SPREP_PROFILE_TEST_MAX_LENGTH];
diff --git a/icu4c/source/test/cintltst/ucnvseltst.c b/icu4c/source/test/cintltst/ucnvseltst.c
index bbb0580fcbd..076120864e0 100644
--- a/icu4c/source/test/cintltst/ucnvseltst.c
+++ b/icu4c/source/test/cintltst/ucnvseltst.c
@@ -30,6 +30,7 @@
 #define TDSRCPATH  ".." U_FILE_SEP_STRING "test" U_FILE_SEP_STRING "testdata" U_FILE_SEP_STRING
 
 static void TestSelector(void);
+void addCnvSelTest(TestNode** root);  /* Declaration required to suppress compiler warnings. */
 
 void addCnvSelTest(TestNode** root)
 {
diff --git a/icu4c/source/test/intltest/ssearch.cpp b/icu4c/source/test/intltest/ssearch.cpp
index c95768cb519..a48648b8a9f 100644
--- a/icu4c/source/test/intltest/ssearch.cpp
+++ b/icu4c/source/test/intltest/ssearch.cpp
@@ -1561,7 +1561,7 @@ const char *cPattern = "maketh houndes ete hem";
          //j = (j + i)%5;
     }
 
-    printf("%d, %d\n", pm-longishText, j);
+    printf("%ld, %d\n", pm-longishText, j);
 #ifndef TEST_BOYER_MOORE
     usearch_close(uss);
 #else
diff --git a/icu4c/source/tools/pkgdata/pkgdata.cpp b/icu4c/source/tools/pkgdata/pkgdata.cpp
index f45be294e88..3a101ce9150 100644
--- a/icu4c/source/tools/pkgdata/pkgdata.cpp
+++ b/icu4c/source/tools/pkgdata/pkgdata.cpp
@@ -215,7 +215,7 @@ enum {
 };
 static char libFileNames[LIB_FILENAMES_SIZE][256];
 
-static void pkg_checkFlag(UPKGOptions *o);
+static UPKGOptions  *pkg_checkFlag(UPKGOptions *o);
 
 const char options_help[][320]={
     "Set the data name",
@@ -1271,7 +1271,7 @@ static int32_t pkg_createWindowsDLL(const char mode, const char *gencFilePath, U
 }
 #endif
 
-static void pkg_checkFlag(UPKGOptions *o) {
+static UPKGOptions *pkg_checkFlag(UPKGOptions *o) {
 #ifdef U_AIX
     /* AIX needs a map file. */
     char *flag = NULL;
@@ -1372,6 +1372,9 @@ static void pkg_checkFlag(UPKGOptions *o) {
         }
     }
 #endif
+    // Don't really need a return value, just need to stop compiler warnings about
+    // the unused parameter 'o' on platforms where it is not otherwise used.
+    return o;   
 }
 
 static void loadLists(UPKGOptions *o, UErrorCode *status)
diff --git a/icu4c/source/tools/toolutil/pkg_genc.h b/icu4c/source/tools/toolutil/pkg_genc.h
index 3c23d3d8b41..750b363a366 100644
--- a/icu4c/source/tools/toolutil/pkg_genc.h
+++ b/icu4c/source/tools/toolutil/pkg_genc.h
@@ -10,7 +10,7 @@
 #include "unicode/utypes.h"
 
 U_INTERNAL void U_EXPORT2
-printAssemblyHeadersToStdErr();
+printAssemblyHeadersToStdErr(void);
 
 U_INTERNAL UBool U_EXPORT2
 checkAssemblyHeaderName(const char* optAssembly);