77 epileptics receiving a combination of anticonvulsants have been studied. 25(OH)D3 levels were diminished in 38% of the patients, markedly so in 25%. iPTH levels were elevated in 13%. Total, as well as ionized, serum calcium levels were significantly lower in the epileptic patients, as compared with a control population. Serum P, Mg, and plasma total CO2 levels remained unaltered. Alkaline phosphatase levels were increased, as well as gamma-GT levels. A transiliac bone biopsy was performed in 15 patients and histomorphometric studies were achieved on decalcified and undecalcified sections. Osteomalacia was present in 4 out of the 15 cases, hyperosteoidosis in one. Three biological features distinguished the cases with osteomalacia : iPTH levels and alkaline phosphatase values were significantly higher, and serum P levels were significantly lower (all were below 2,4 mg/dl) as compared with the non-osteomalacic patients. In an epileptic population, the serum Ca value is lower than in a control population by 0,5 mg/dl. When in addition the serum P is low (which was a feature of male patients), the danger exists for osteomalacia to develop. The former abnormality is connected with low 25(OH)D3 levels, the primary event, while the latter is probably related to high (secondary) iPTH levels.