A total of 152 severely mentally and physically handicapped children were studied with regard to severity of bone atrophy assessed by microdensitometry (MD) and serum levels of calcium (Ca), phosphorus (P), alkaline-phosphatase (Al-P) and Vitamin D metabolites in an intra-group comparative manner. They were divided into four groups; MA: mobile and anticonvulsant-receiving (58 cases), MN: mobile and anticonvulsant-non-receiving (48 cases), NA: immobile and anticonvulsant-receiving (27 cases), and NN: immobile and anticonvulsant-non-receiving (17 cases). Microdensitometric (MD) abnormalities were noted in about 80% of patients. MD parameters were worse in the immobile groups than in the mobile groups. Serum levels of Ca were significantly lower, and those of Al-P were significantly higher in the anticonvulsant-receiving groups than the anticonvulsant nonreceiving groups. The serum level of 25-hydroxyvitamin D (25-0H-D) was low in all groups. Fifty-eight children with MD abnormalities were treated with 1 α-OH-D3, and MD and hematological findings were improved specially in the mobile groups. This means that mobility plays an important role in the progress of osteopathy and treatment of severely mentally and physically handicapped children.