The physiological condition of animals connects resources in the environment to demographic responses through reproduction, survival and abundance, and it provides critical information for conservation and management of wildlife populations. We used archived data (early-wet season 1987, late-wet and early-dry season 1988) from culls of impala (Aepyceros melampus) to compare how the kidney fat index (KFI, short-term index of body condition) and carcass mass (long-term index) varied seasonally. For females, KFI increased across seasons, a pattern similar for all age classes. For males, KFI was low and relatively invariable for juveniles and yearlings. For adults, KFI varied with reproductive cycle; highest KFI occurred early in the rut for males and around the second trimester for females. Carcass mass increased over time for growing juveniles and yearlings. For adults, female carcass mass varied according to reproductive cycle and was highest when KFI was highest. Male carcass mass was highest toward the end of the rut when KFI was relatively low. Although changes in body condition can be associated with seasonal changes in forage and activity, KFI and carcass mass are most useful when comparing across years with varying conditions, but within age, sex, and season.