In 20 female patients treated for 2 to 37 years (mean :12) with anticonvulsant drugs, low serum levels of 25-hydroxy-vitamin D (25-OH-D; 6.4 +/- 3.2 ng/ml M +/- SD), relative hypocalcemia (9.2 +/- 0.4 mg/100 ml) and high levels of parathyroid hormone (PTH 277 +/- 165 pg/ml) were found compared to an age-matched control group (respectively 8.6 +/- 3.2 ng/ml, 9.6 +/- 0.3 mg/100 ml and 183 +/- 95 pg/ml) living in the same psychiatric clinic. A significant negative correlation was found between total duration of treatment and either serum 25-OH-D or serum calcium. After treatment with an oral vitamin D3 supplement (2000 IU/day) for 3 weeks, the serum 25-OH-D levels, although increased, remained lower than normal in the epileptic group and neither hypocalcemia nor their secondary hyperparathyroidism were corrected. These data confirm the occurrence of vitamin D deficiency in patients treated with anticonvulsant drugs resulting in hypocalcemia and secondary hyperparathyroidism.