Obesity has been linked to lower serum 25-hydroxyvitamin D [25(OH)D] values, but whether this relationship plays a role in the poorer vitamin D status observed in blacks vs. whites is not clear. This study examines the relationship between serum 25(OH)D and percent body fat (%BF) by race in 6042 women (3567 non-Hispanic whites and 2475 non-Hispanic blacks), aged 12+ yr, from the third National Health and Nutrition Examination Survey (NHANES III, 1988-1994). Serum 25(OH)D values were measured with an RIA kit (DiaSorin), and %BF was calculated from bioelectrical impedance analysis. Adjusting for %BF only slightly reduced differences in mean serum 25(OH)D by race. The negative relationship between serum 25(OH)D and %BF was noticeably stronger in whites than in blacks of the same age. Within race, the relationship was stronger in younger than older individuals. Adjusting for confounders reduced, but did not remove, these differences in relationship strength. In conclusion, the serum 25(OH)D-%BF relationship in women varies both by race (stronger in whites than blacks) and age (stronger in younger than older persons). This complex relationship may explain why differences in obesity do not appear to play a major role in explaining variation in serum 25(OH)D by race.