Fibrodysplasia ossificans progressiva in children can often be recognized at birth because of the presence of shortening of the great toe, characteristic hallux valgus, and short thumbs. The majority of patients have the onset of symptoms by the age of four years, but there is often a delay of many months before the diagnosis is made. Early recognition will allow protection of the child from injuries in which the damaged tissue will serve as a focus of calcification. Most patients with this condition are physically disabled. The site of onset and of greatest involvement is axial. Biopsy and surgery are best avoided. Use of EHDP (disodium ethane 1-hydroxy, 1-diphosphonate, or disodium etidronate) is not as yet of proved value in most patients. Data from this study support the concept that most cases of this lesion arise as dominant mutations.