We describe the fission of one large East African clan of spotted hyenas (Crocuta crocuta). During an 8-mo period from late 1989 to early 1990, 8 of 22 adult females vanished from the clan, along with their juvenile offspring. 6 of these 8 adult females formed a new clan in an area adjacent to the parent clan's home range. The 6 adult female dispersers belonged to three mid- or low-ranking matrilines in the parent clan. Two juvenile males returned to the parent clan for temporary visits, and three female members of one matriline rejoined the parent clan after absences of over 8 mo. Returning females, but not males, were targets of severe aggression by adult female residents of the parent clan, and by juvenile residents of both sexes. Returning females fell from their previous mid-ranking positions to the bottom of the adult female hierarchy. Our data suggest that clan fission was promoted by the simultaneous occurrence of low food availability, an unusually high density of higher-ranking conspecific competitors, and the availability of neighboring vacant habitat.