Percent body fat was estimated from the Kidney Fat Index for 1,726 male, white-tailed deer from the Savannah River Plant in South Carolina for the years 1974 through 1978. There was a significant decrease in percent body fat from September through December in all animals ≥2.5 years. Percent fat in fawns increased significantly from September through December. Fat levels in 1.5-year-old animals did not show a general trend for either an increase or decrease from September through December. However, the lowest percent fats were consistently observed in November for all but the 0.5-year-old males: Percent body fat was significantly related to body weight, month of collection, and age of the male, but the multiple coefficient of determination was small for this relationship (R2 =0.09). The rapid change in fat levels in males during the breeding season indicates that caution must be exercised when using the kidney fat index as a management tool. Management decisions derived from the use of KFI should be based upon animals collected at the same time of the year and of the same sex and age class. Low fat levels in older males during the breeding season are primarily a result of breeding activity.