No report has confirmed predation on wild chimpanzees by lions. Recently, at least two lions visited the Mahale Mountains National Park, Tanzania. Chimpanzee remains, including hairs, bones, and a tooth, were found in four samples of lion feces between June and September 1989. The discovery of each fecal sample, widely separated in time, combined with analyses of daily attendance records and fecal contents, suggests that at least four chimpanzees, including two adult females, an old adolescent male, and an early adolescent male, were eaten. Observed responses of chimpanzees to lions included alarm calls, whimpers, climbing into trees, and silence. Predation by lions has been neglected as a factor shaping the social structure of chimpanzees. Nevertheless, the large party size that has often been observed in savanna-living chimpanzees, which are sympatric with lions, might be an anti-predator response of this species. © 1993 Wiley-Liss, Inc.