Eight hundred patients with alopecia areata (AA) responded to a detailed questionnaire that was compiled, distributed, and analyzed by Help Alopecia International Research, Inc. (HAIR). Among those responding, 28% were men and 72% were women. Fifty percent had localized alopecia, 30% had alopecia totalis, and 20% had alopecia universalis. Forty-eight percent developed their initial onset before the age of 20. A very strong family history of 42% was found. There were 333 additional family members with AA. Many patients and relatives had concurrent atopic diseases (seasonal rhinitis, bronchial asthma, and atopic dermatitis). Associated autoimmune diseases including vitiligo, thyroid disease, and collagen vascular disease in patients and relatives appeared consistent with previous reports. Insulin dependent diabetes mellitus (IDDM) was not increased in patients but greatly increased in relatives. Additional analysis suggests a genetic association between the two diseases where expression of AA may prevent the development of IDDM.