Previous studies have shown differences between African-American and Caucasian populations in the prevalence of obesity and obesity-related diseases such as type IIoffabetes. The purpose of this study was (1) to compare the insulin sensitivity index (SI) from the minimal model in 37 African-American and 22 Caucasian women matched for age and obesity, and (2) to determine whether the relationship between intraabdominal fat distribution and SI (and other health risk factors) was similar in both races. To address the second question, intraabdominal fat distribution was assessed by computed tomographic (CT) scans in a subset of 23 African-American and 15 Caucasian women. Despite having a similar body mass index ([BMI] weight in kilograms divided by height in meters squared) and waist to hip ratio (WHR), African-American women had a mean SI value that was approximately 36% lower than in the Caucasian women (3.45 +/- 0.42 v 5.40 +/- 0.55 x 10(-5) min(-1) / pmol x L, P = .007). Visceral fat area was smaller in African-American women (98.0 +/- 8.5 CM2) than in Caucasian women (117.3 +/- 12.4 CM2) despite similar BMI and WHR. Visceral fat area was strongly correlated with WHR in the Caucasian women (r = .76, P < .001), as previously observed, but not in the African-American women (r = .24, NS). WHR was significantly correlated with fasting insulin and serum cholesterol in the Caucasian women but not in the African-Americans. Visceral fat was correlated with metabolic risk factors in both groups, but subcutaneous abdominal fat was significantly correlated with SI and fasting insulin only in the African-American women. These results suggest that the relationship between body fat distribution and health risk factors may be different in African-Americans and Caucasians. Additionally, reduced insulin sensitivity in African-American women may in part explain the high diabetes rate in this population.