diff --git a/icu4c/source/test/intltest/numfmtst.cpp b/icu4c/source/test/intltest/numfmtst.cpp
index bc9fc7fcb8a..484f16bee71 100644
--- a/icu4c/source/test/intltest/numfmtst.cpp
+++ b/icu4c/source/test/intltest/numfmtst.cpp
@@ -241,6 +241,7 @@ void NumberFormatTest::runIndexedTest( int32_t index, UBool exec, const char* &n
   TESTCASE_AUTO(Test20358_GroupingInPattern);
   TESTCASE_AUTO(Test13731_DefaultCurrency);
   TESTCASE_AUTO(Test20499_CurrencyVisibleDigitsPlural);
+  TESTCASE_AUTO(Test13735_GroupingSizeGetter);
   TESTCASE_AUTO_END;
 }
 
@@ -9705,4 +9706,24 @@ void NumberFormatTest::Test20499_CurrencyVisibleDigitsPlural() {
     }
 }
 
+void NumberFormatTest::Test13735_GroupingSizeGetter() {
+    IcuTestErrorCode status(*this, "Test13735_GroupingSizeGetter");
+    {
+        DecimalFormat df("0", {"en", status}, status);
+        assertEquals("pat 0: ", 0, df.getGroupingSize());
+        df.setGroupingUsed(false);
+        assertEquals("pat 0 then disabled: ", 0, df.getGroupingSize());
+        df.setGroupingUsed(true);
+        assertEquals("pat 0 then enabled: ", 0, df.getGroupingSize());
+    }
+    {
+        DecimalFormat df("#,##0", {"en", status}, status);
+        assertEquals("pat #,##0: ", 3, df.getGroupingSize());
+        df.setGroupingUsed(false);
+        assertEquals("pat #,##0 then disabled: ", 3, df.getGroupingSize());
+        df.setGroupingUsed(true);
+        assertEquals("pat #,##0 then enabled: ", 3, df.getGroupingSize());
+    }
+}
+
 #endif /* #if !UCONFIG_NO_FORMATTING */
diff --git a/icu4c/source/test/intltest/numfmtst.h b/icu4c/source/test/intltest/numfmtst.h
index 66c4b2d9c73..78bdf645409 100644
--- a/icu4c/source/test/intltest/numfmtst.h
+++ b/icu4c/source/test/intltest/numfmtst.h
@@ -297,6 +297,7 @@ class NumberFormatTest: public CalendarTimeZoneTest {
     void Test20358_GroupingInPattern();
     void Test13731_DefaultCurrency();
     void Test20499_CurrencyVisibleDigitsPlural();
+    void Test13735_GroupingSizeGetter();
 
  private:
     UBool testFormattableAsUFormattable(const char *file, int line, Formattable &f);
diff --git a/icu4j/main/tests/core/src/com/ibm/icu/dev/test/format/NumberFormatTest.java b/icu4j/main/tests/core/src/com/ibm/icu/dev/test/format/NumberFormatTest.java
index 9f2adec4244..2b5c2f2c1e2 100644
--- a/icu4j/main/tests/core/src/com/ibm/icu/dev/test/format/NumberFormatTest.java
+++ b/icu4j/main/tests/core/src/com/ibm/icu/dev/test/format/NumberFormatTest.java
@@ -6669,4 +6669,25 @@ public class NumberFormatTest extends TestFmwk {
             assertEquals("iteration " + i, expected, actual);
         }
     }
+
+    @Test
+    public void test13735_GroupingSizeGetter() {
+        DecimalFormatSymbols EN = DecimalFormatSymbols.getInstance(ULocale.ENGLISH);
+        {
+            DecimalFormat df = new DecimalFormat("0", EN);
+            assertEquals("pat 0: ", 0, df.getGroupingSize());
+            df.setGroupingUsed(false);
+            assertEquals("pat 0 then disabled: ", 0, df.getGroupingSize());
+            df.setGroupingUsed(true);
+            assertEquals("pat 0 then enabled: ", 0, df.getGroupingSize());
+        }
+        {
+            DecimalFormat df = new DecimalFormat("#,##0", EN);
+            assertEquals("pat #,##0: ", 3, df.getGroupingSize());
+            df.setGroupingUsed(false);
+            assertEquals("pat #,##0 then disabled: ", 3, df.getGroupingSize());
+            df.setGroupingUsed(true);
+            assertEquals("pat #,##0 then enabled: ", 3, df.getGroupingSize());
+        }
+    }
 }