The investigation of biochemical alterations in vitamin D metabolism was undertaken in institutionalized epileptic patients receiving anticonvulsant therapy. The influencing factors assessed included : anticonvulsant therapy, U.V. exposure, diet, and mobility. The epileptic group was compared to a group of non epileptic institutionalized patients and a group of normal healthy controls. Calcium and alkaline phosphatase were significantly altered in the epileptic group compared to the other two groups. However 250 HD levels were similarly reduced in the two institutionalized groups compared to controls. U.V. exposure, diet and mobility influenced vitamin D metabolism, however anticonvulsants had a more severe effect on bone mineral metabolism. © 1986 Springer.