A special exemption from the 1986 Age Discrimination Act allowed colleges and universities to enforce mandatory retirement of faculty at age 70 until 1994. We compare faculty turnover rates at a large sample of institutions before and after the federal law change, and at a set of institutions that were covered by earlier state laws prohibiting compulsory retirement. Retirement rates at institutions that enforced mandatory retirement exhibited sharp ?spikes? at ages 70 and 71. About 90 percent of professors who were still teaching at age 70 retired within two years. After the elimination of compulsory retirement the retirement rates of 70 and 71-year-olds fell to levels comparable to 69- year-olds, and over one-half of 70-year-olds were still teaching two years later. These findings indicate that U.S. colleges and universities will experience a rise in the number of older faculty over the coming years. The increase is likely to be larger at private research universities, where a higher fraction of faculty has traditionally remained at work until age 70.