A clinical study showed that the frequency of diabetic hypertension, estrogen effect in the vaginal smear and proliferative changes of the endometrium were significantly higher in patients with endometrial cancer than in a control group (P .ltoreq. 0.001). Obesity was also significantly more frequent (0.02 < P < 0.01). In vitro studies demonstrated a significantly higher aromatization of androstendione to estrone in adipose tissue of endometrial cancer patients (P < 0.01), indicating etiologic correlations between endometrial cancer and extraglandular estrone production. An additional clinical study indicated a better 5-yr survival rate if parameters indicating endogenous estrogen effects were present.