Dual energy X-ray absorptiometry (DXA) was used to assess lumbar spine (L2-4) and femoral neck bone mineral density (BMD) in 36 children taking either carbamazepine or valproic acid for longer than one year, for generalized idiopathic epilepsy. Patients were matched with controls. Biochemical parameters of bone mineral metabolism were also measured. BMD values at both the femur neck and lumbar spine in both the carbamazepine and valproic acid groups were not significantly different from that of the control group. Serum levels of calcium were subnormal and alkaline phosphatase levels were high in the carbamazepine group. Urinary calcium levels were significantly lower in both groups than in the control group (p< or =0.05) and also significantly lower in the valproic acid group than in the carbamazepine group (p< or = 0.05). There were no other significant biochemical changes in either group. In conclusion, the results suggest that valproic acid and carbamazepine monotherapies have minimal effects on bone mineral metabolism, but routine monitoring of risk and consideration of prophylactic vitamin D supplementation is important.