Securities laws prohibit open-end mutual funds from borrowing more than one-third of their capital structure because of concerns that too much borrowing may harm investors. This is the first article to examine the performance of open-end funds that borrow money within these permissible limits. We construct a database from annual filings of open-end domestic equity mutual funds covering 17 years from 2000 to 2016. Eighteen percent of funds borrowed money for leverage within that time. We find that borrowing funds underperform their nonborrowing peers by 62 basis points per year on a total return basis, while also incurring greater risk. After accommodating for the greater risk taking, we find that borrowers underperform by 48 to 72 basis points annually. By contrast, funds that use derivatives and other financial instruments perform about as well as unlevered mutual funds, before and after adjusting for risk, and with less volatility. This suggests that many mutual funds use derivatives to hedge risk rather than as a substitute for leverage through the capital structure. Thus borrowing may present a greater risk than derivatives, which have received more attention than borrowing. Fund investors and regulators would benefit from greater transparency into mutual fund capital structure.Mutual Funds that Borrow 769