Reports of hypovitaminosis D associated with anticonvulsant drugs in pediatric patients are conflicting. The effects of carbamazepine or sodium valproate on vitamin D status were evaluated prospectively in 51 ambulatory epileptic children who were followed during the first year of the study and in 25 and 6 children during the second and third year, respectively. Serum 25-hydroxyvitamin D, parathyroid hormone, calcium, and phosphorus levels were determined before and every 3 months during anticonvulsant therapy. Our subjects were grouped into four classes (0, 1, 2, and 3 consisted of the patients before and during the first, second, and third years of the treatment, respectively). The control group consisted of 80 healthy children. Comparisons between controls and patients of class 0 for the means for each season of all variables showed no significant differences. A decreasing trend in serum 25-hydroxyvitamin D (P < .03) and an increasing trend in serum parathyroid hormone (P < .04) levels were noticed in all seasons from class 0 to class 3. Twenty-five patients (49%) acquired hypovitaminosis D during the study period. The effects of seasonality on serum 25-hydroxyvitamin D, parathyroid hormone, and calcium were noticed in our patients grouped in classes 0, 2 and 3, as well as in controls. Evidence is provided that carbamazepine or sodium valproate can cause hypovitaminosis D in children.