One hundred‐twelve endometrial cancer patients and 200 comparison patients were interviewed in New York hospitals. Additionally, the hospital records of more than 900 patients with endometrial cancer were reviewed. The most important factor found related to cancer of the endometrium is obesity. Tallness, in addition to obesity, enhances the risk of endometrial cancer distinctly. Other differences between the cancer patients and the comparison subjects, including late menopause, heavy menstrual bleeding and premenstrual breast swelling, suggest that the etiological basis for endometrial cancer may be increased retention of certain endogenous hormones. The most practical preventive measure for endometrial cancer appears to be an effective reduction in weight although the epidemiological proof of the consequences remains to be given.