In a prospective study of 175 adult Asian patients attending a medical out-patient clinic we found a spectrum of metabolic bone disease. Twenty-four patients (13.5 per cent) had definite osteomalacia, of whom 11 (6 per cent) had severe clinical osteomalacia on the basis of associated symptoms and radiological signs. Fifteen (8.5 per cent) had borderline osteomalacia, while the remaining 136 (78 per cent) had normal bone biopsy, or were presumed to be normal. This histological spectrum was paralleled by the increasing prevalence of musculoskeletal symptoms (thigh pain, change in gait and difficulty rising from seated position) attributable to osteomalacia. Multivariate analysis showed that the major determinant of osteomalacia in Asians in South London was vegetarian diet. Increasing severity of bone disease was associated with increasingly strict vegetarian practice, which accounted for the excess risk of females, Hindus, and Asians originating from East Africa. Covering skin when outdoors also contributed to the female excess risk, and suggested a role for reduced solar exposure. Clinically significant osteomalacia is underdiagnosed in the Asian population, but evidence of dietary adaptation suggests this problem may diminish with time.