Using a unique data set of detailed balance sheet information on mutual funds, we find that most mutual funds using derivatives do so to a very limited extent that has little discernable impact on returns. However, there exist two types of funds that make more extensive use of derivatives, global funds and specialized domestic equity funds. The risk and return characteristics of these two groups of funds are significantly different from funds employing derivatives sparingly or not at all. Fund managers time their use of derivatives in response to past returns. Evidence during the financial crisis of August 1998 supports the hypothesis that the effects of derivative use are most pronounced during the periods of extreme movement. © 2010 Wiley Periodicals, Inc. Jrl Fut Mark 31:629–658, 2011