Atraumatic fractures are often seen in children and adolescents with cerebral palsy (CP) and epilepsy in full-time care. Increased bone fragility was postulated to be due to osteopenia resulting from a combination of factors including immobilization and antiepileptic treatment. The aim of this study was to determine the effect of vitamin D and calcium substitution on bone mineral density (BMD) in a group of children with CP in full-time care. Twenty children with the most severe form of CP (spastic quadriplegia) who had been treated with antiepileptic drugs for a relatively long period of time were included in the study. Physical examination and laboratory analyses excluded other possible causes of osteopenia. BMD was measured by dual X-ray absorptiometry. Thirteen patients were treated for 9 months with 1,25-dihydroxy-cholecalciferol vitamin D (0.25 mcg daily) and with calcium (500 mg daily). Seven control children were used for observation only. BMD greatly increased in the treated group, while children with CP in full-time care who did not receive vitamin D and calcium substitution continued to lose their bone mass. It can be concluded that the addition of vitamin D and calcium increases BMD in children with the most severe form of CP, who are receiving antiepileptic drugs.