Diabetic women may have an increased risk of developing endometrial carcinoma. Ovarian and adrenal activity seem to be factors in the genesis of this cancer. We have measured serum sex hormone-binding globulin (SHBG), free and bound fractions of estrogens and androgens, and gonadotropins in 20 consecutive postmenopausal insulin-treated diabetic women and 16 normal postmenopausal women. The diabetics were nonketoacidotic, without nephropathy and without proliferative retinopathy. The groups were comparable regarding age and percent ideal body weight. The diabetic group had significantly increased serum levels of estrone (P less than 0.001), estrone sulfate (P less than 0.05), 17 beta-estradiol (P less than 0.02), and SHBG (P less than 0.001). Levels of testosterone, delta 4-androstenedione, and dehydroepiandrosterone sulfate tended to be higher (not significantly) in the diabetics. FSH and LH levels were similar in the two groups, while serum PRL was significantly lower in the diabetic group (P less than 0.02). The hormonal changes in the diabetics were not related to control of the diabetes. We conclude that total estrogen levels are increased in postmenopausal women with insulin-treated diabetes mellitus. High SHBG levels in these patients tend to keep the free fractions of sex hormones within normal limits.