The annual reproductive cycle of a captive colony of Barbary apes, Macaca sylvana, was examined for the 26-year period from 1950 to 1976 and then compared with the annual reproductive cycle of semifree ranging M.sylvania in Gibraltar. Mating and birthing seasons for the two populations were similar although birth synchrony was more pronounced in the Gibraltar colony. The environmental factors influencing the maintenance of the annual cycles in both localities are examined.