Epidemiologic studies of alopecia areata (AA) are available from USA, Japan and European countries, but there is a paucity of literature on AA from Asian countries, especially from the Indian subcontinent. In a prospective, hospital-based study lasting for a decade (1983-1992), the epidemiology of AA was studied, including associated diseases and risk factors for development of severe AA. Simultaneously a similar study was carried out in age- and sex-matched controls. Eight hundred and eight patients (532 men, 276 women) and 572 age- and sex-matched controls (370 men, 202 women) were studied. The incidence of AA was 0.7% of new dermatology outpatients. The majority of patients (712, 88%) were below 40 years of age, including 196 children < 16 years of age (24%). Almost half (46%) of the women patients had onset of AA in childhood, compared to only 19% in men (P < 0.001). Alopecia was total, universal, or extensive in 154 patients (19%). An onset in the first two decades was more often associated with severe alopecia (P < 0.001), especially in men (P < 0.01). Alopecia areata was recorded in family members of 70 patients (9%), being more frequent in the severe forms of AA (16%). Evidence of atopy was recorded in a total of 146 instances (18%). The frequency of atopy was the same in circumscribed alopecia (18.1%) and severe alopecia (18.2%). Nail changes were found in 162 patients (20%) and were more frequent in 76 (47%) with the severe form of AA (P < 0.001). On 39 occasions (5%), autoimmune-related diseases were detected: vitiligo in 15 (1.8%), thyroid disorders in 8 (1%), lichen planus in 6 (0.7%), collagen vascular diseases in 5 (0.6%), diabetes mellitus in 4 patients (0.4%), and pemphigus foliaceus in 1 (0.1%) patient. Patients with family members having vitiligo (recorded in 5.9% of patients), were more frequently affected with severe alopecia (P < 0.001). Alopecia areata in North Indians showed a preponderance in men (M:F = 2:1) and the majority of persons with disease (88%) were below 40 years of age. Onset in childhood was more frequent in girls or women, but the incidence of severe alopecia was higher in boys or men with onset at an earlier age. Diseases associated with autoimmunity were seen in only 5% of patients. Atopy was found to be associated in 18% of patients, but its reported association with younger age of onset and severe alopecia was not confirmed. Presence of vitiligo in family members and onset before 20 years of age, especially in boys or men, were found to be risk factors for severe alopecia.