The relationship between non-insulin-dependent diabetes mellitus (NIDDM) and body fat distribution (BFD) as measured by waist/hip circumference (WHR) was investigated in a Navajo community. A sample of 136 females and 89 males, 20 years and older, was recruited using a cluster-sampling design. Fifty percent of the females and 30.3% of the males are overweight [body mass index (BMI) equivalent of >120% ideal body weight]. Prevalence of NIDDM is 14% in females and 10.1% in males. The sample is characterized by central BFD (mean WHR=0.897ยฑ0.075, females and mean WHR=0.963ยฑ0.071, males). WHR is significantly related to age and BMI in males (P < 0.05), but not in females. Adjusted odds ratios for risk of NIDDM prevalence with increasing WHR category were estimated from a multiple logistic regression model which controlled for age and BMI. The odds ratio and 95% confidence interval (95% CI) is 2.19 (1.14, 4.19) for risk of NIDDM prevalence for a female in the middle BFD category compared to a female in the low BFD category. Risk increases to 3.63 (95% CI=1.25, 10.52) for a female in the highest BFD category. Although there is an increased risk of NIDDM prevalence with central BFD for males, it is not statistically significant. Preferential energy storage in abdominal fat depots may be a phenotypic expression of the "Thrifty Genotype," which places American Indians at greater risk for metabolic disorders.