Diabetic retinopathy rarely occurs before puberty, suggesting that changes in sex hormones may influence the development of this condition. The authors measured serum testosterone, estradiol, DHEA-S, and sex hormone binding globulin levels in 26 men and 22 women with type I diabetes from the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR), a population-based study of diabetic complications. The mean age was 23 years and the mean duration of diabetes was 14 years. Subjects with proliferative or preproliferative retinopathy (greater than or equal to retinopathy level 51-80) were matched by duration of diabetes (+/- 2 years) and sex to subjects with minimal or no retinopathy (less than or equal to retinopathy level 21). Seven stereoscopic retinal photographs of each eye were obtained and photographs were read by the University of Wisconsin Reading Center. Serum testosterone concentrations were significantly higher in male diabetic subjects with proliferative retinopathy (648 +/- 36 ng/dl) than in male diabetic subjects with minimal or no retinopathy (512 +/- 43 ng/dl) (P = 0.017). No other statistically significant differences in sex hormones between subjects with and without proliferative retinopathy were observed. Although these results should be regarded as preliminary because of the small number of subjects, they support the hypothesis that testosterone concentrations may be associated with the development of retinopathy in type I diabetic patients.