A review of 50 adult epileptics who had taken anticonvulsant drugs for 10 or more years showed a decrease in the concentration of serum phosphate and calcium and an increase in the activity of alkaline phosphatase in 22% of the patients. Plasma albumin and gamma-globulin levels were higher than in control subjects. All the patients lived at home and the dietary intake of calcium and vitamin D was often borderline normal or low. Six patients were submitted to bone biopsy and of these, 4 showed histological osteomalacia. Gastrointestinal disease did not appear to be a significant factor. None of the patients had symptoms or signs attributable to osteomalacia which does not seem to be of serious significance. All the patients were taking at least two drugs and it was not possible to assess the relative importance of the various drugs. A prospective study is needed. Measurements of serum calcium, phosphorus, and alkaline phosphatase should be performed at intervals on patients who are receiving anticonvulsant therapy. Treatment with calciferol may be indicated.