Juvenile chimpanzees at Gombe National Park associated almost constantly with their mothers for several years after they were weaned from suckling. Then this association declined abruptly in three contexts: (1) when mothers resumed oestrous cycles and consorted with individual males, (2) when females left their mothers at adolescence to mate with males, (3) when males reached puberty. Males spent more time at a distance from their mothers and were more gregarious than females. Mothers supplanted daughters more than sons from food. The contexts of separation and the positive interactions between mothers and offspring of all ages suggest that conflicting social requirements rather than increased rejection by the mother eventually draw mother and offspring apart. The costs and benefits to mothers and offspring of continued association are discussed in the context of the unusual social structure of chimpanzees. © 1983.