Territorial aggression in a lek breeding population of white-eared kob (Kobus kob leucotis) was investigated in the Boma National Park region, southern Sudan. The frequency of aggression on leks was positively related to the number of females present, but generally declined over the course of the breeding season. Males fought most strenuously for central territories that were preferred by females. Males with females in their territories were more frequently engaged in fights than unaccompanied males. Such fights often induced females to leave their original partners, especially when large groups of females were involved. Territorial aggression led to damaging injuries in several instances, and mortality of breeding age males was disproportionately high. These results suggest that the intensity of aggression exhibited by territorial males was scaled to potential reproductive benefits.