The mating behavior of female Barbary macaques (Macaca sylvanus) has been called "promiscuous" because females mate with multiple males in rapid succession. The data presented here, based on a 9 month study of a semifree-ranging colony, supports the idea that females do indeed mate indiscriminately and at a high rate. Five hundred six copulations were recorded for 21 females during the breeding season, and 358 of these copulations occurred when females were in extended estrous cycles. As the days that females spent in estrus increased, either because they had longer cycles or more cycles than some other females, the number of different male partners also increased. There was no association between mating behavior and either male-female friendships or male care of infants born the following birth season. Promiscuity cannot be explained by selection to confuse paternity. There is also no evidence that females exchange copulations for support or affiliation. Female Barbary macaques mate with multiple males because males are unable, or are unwilling, to stop them.