selecting duplicate rows

Ever wondered how to select only rows that have some duplicate from a field? Well, here is one way that worked pretty well:

select duplicate_column from table_with_duplicates where
(
   select count(a.duplicate_column) from table_with_duplicates a
   where a.duplicate_column = table_with_duplicates.duplicate_column
) > 1
group by duplicate_column

Hope that helps someone.