Camurati-Engelmann disease is characterized by hyperostosis of the long bones and the skull, muscle atrophy, severe limb pain, and progressive joint contractures in some patients. It is caused by heterozygous mutations in the transforming growth factor beta 1 (TGF beta 1) believed to result in improper folding of the latency-associated peptide domain of TGF beta 1 and thus in increased or deregulated bioactivity. Losartan, an angiotensin II type 1 receptor antagonist, has been found to downregulate the expression of TGF beta type 1 and 2 receptors. Clinical trials with losartan have shown a benefit in Marfan syndrome, while trials are underway for Duchenne muscular dystrophy and other myopathies associated with TGF beta 1 signaling. We hypothesized that due to its anti-TGF beta 1 activity, losartan might be beneficial in Camurati-Engelmann disease. This report concerns a boy who presented at age 13 years with severe limb pain and difficulty in walking. Clinical and radiographic evaluation results were compatible with Camurati-Engelmann disease and the diagnosis was confirmed by mutation analysis (c.652C>T[p.Arg218Cys]). The boy underwent an experimental treatment with losartan at a dosage of 50 mg/day, orally. During the treatment period of 18 months, the intensity and frequency of limb pain decreased significantly (as shown by a pain diary), and muscle strength improved, allowing the boy to resume walking and climbing stairs. No obvious side effects were observed. We cautiously conclude that TGF beta 1 inhibition with losartan deserves further evaluation in the clinical management of Camurati-Engelmann disease. (C) 2014 Wiley Periodicals, Inc.