Difference in Join syntax between SQL 2005 and SQL 2008

I am upgrading my SQL database from 2005 to 2008. I am having difficulty with LEFT OUTER JOINS. In 2005 it joins the first table to each matching record on the second table. In 2008 it is only returning each row from the first table once and returning NULL values for the second table as there are multiple matches. Can anyone help please?