A case-control study was undertaken to evaluate the roles of obesity and body fat distribution in the etiology of endometrial cancer. The study also included an evaluation of the associations of serum estrone, estradiol, and androstenedione with obesity, body fat distribution, and endometrial cancer risk. The study included 168 cases and 334 control subjects identified at an optometry clinic. A strong, positive relationship between overall obesity and endometrial cancer was found. The relative rate of endometrial cancer for women in the upper 90th percentile of a body mass index compared to those below the median was estimated as 5.5 with 95% confidence limits of 3.2-9.6. There was no association between endometrial cancer and the waist to hip ratio, an index of upper versus lower body fat distribution. A statistical test of trend across the four quartiles of the waist to hip ratio yielded a P value of 0.45 after adjustment for confounding by the body mass index. On the other hand, there was a statistically significant, independent positive effect of a high subscapular to tricep skinfold ratio, a measure of central versus peripheral obesity, on endometrial cancer risk. The relative rates of endometrial cancer for the second, third, or fourth quartile compared to the first quartile of this index were 1.5, 1.9, and 2.7, respectively (P = 0.007), after adjustment for the body mass index. Serum estrone and estradiol, but not androstenedione, were statistically significantly correlated with the body mass index among control subjects (r = 0.37 and 0.40 for estrone and estradiol, respectively). On the other hand, each of the sex hormones was uncorrelated with the waist to hip ratio after adjustment for body mass. The correlations between each of the three hormones and the subscapular to tricep skinfold ratio among controls were weak and were not statistically significant (0.10, 0.10, and 0.14 for estrone, estradiol and androstenedione, respectively). Cases had statistically significantly higher mean serum estrogen and androstenedione levels than did controls and these elevations did not simply reflect a higher prevalence of obesity among them. The findings are equivocal with respect to fat patterns and endometrial cancer. We suggest that future epidemiological studies of cancer and body fat distribution more carefully distinguish among the various types of fat patterns.