A boy with fibrodysplasia ossificans progressiva received nearly twice the usual therapeutic dose of disodium etidronate for 13 months in an attempt to prevent reossification following a second operation to correct severe torticollis. The operation was successful, but during therapy he developed weakness and distinctive bone lesions characterized by general osteopenia, widened physes, and unique radiolucent bands in the metaphyses. The osseous abnormalities were distinct from those of rickets and healed after withdrawal of the drug.