To study the association between anticonvulsant therapy and osteomalacia or rickets, we evaluated 450 epileptic patients receiving anticonvulsants and residing in an institution for the mentally retarded in Florida. Fifty-five of them with increased mean serum alkaline phosphatase and mildly depressed mean serum calcium levels were identified as being at risk for having osteomalacia. None of them, however, had low serum levels of vitamin D (25[OH]D) or radiologic evidence of osteomalacia or rickets. In contrast to reports from northern climates, we found minimal evidence of anticonvulsant-induced bone disease. The study suggests that exposure to sunshine in our patients probably prevented the development of anticonvulsant-induced osteomalacia or rickets.