There is no known effective therapy for fibrodysplasia ossificans progressiva. Ethane-1-hydroxy-1-diphosphonate has been studied because of its inhibitory effect on bone mineralization and its potential to impair the rapid ossification process observed after acute episodes of fibrodysplasia ossificans progressiva. In an open study, the effects of intravenously administered ethane-1-hydroxy-1-diphosphonate and oral corticosteroids in the treatment of fibrodysplasia ossificans progressiva was evaluated. Thirty-one fibrodysplasia ossificans progressiva attacks were observed in seven patients during the mean followup of 6 years. In 29 attacks, the authors observed a rapid diminution of local inflammation, swelling, and pain during the first 7 days of treatment. However, despite the ethane-1-hydroxy-1-diphosphonate treatment, 10 new ossifications were observed, causing severe deterioration of joint mobility in all affected patients. In 21 attacks, no new ectopic ossification appeared. The radiologic pattern of preexisting ossifications did not change during the treatment. There are no data in the literature describing the percentage of acute episodes leading to an ossification. The results suggest the possibility that intravenous administration of ethane-1-hydroxy-1-diphosphonate and oral steroids may be helpful for the treatment of fibrodysplasia ossificans progressiva, but more control data on the spontaneous resolution of early flareups are needed.