A multicenter study on fibrous dysplasia of bone (FD) was promoted by the European Pediatric Orthopaedic Society in 1999 in order to gain insight into the natural history of the disease and to evaluate current diagnostic and therapeutic approaches. We collected and reviewed clinical, radiographic, pathological, and molecular genetic data when possible, from a total of 64 cases diagnosed as either monostotic FD (MFD), polyostotic FD (PFD), or McCune-Albright syndrome (MAS), evaluated or treated in 11 participating centers. Results from the initial analysis of the series indicate five main points: (1) Significant diagnostic pitfalls affect the diagnosis of MFD and, to a lesser extent, PFD in orthopedic centers and allied radiology and pathology facilities, which may be circumvented by the adoption of stringent diagnostic criteria, and in some cases by the analysis of FD-associated GNAS1 mutations. (2) MFD carries a significant risk for fracture in the face of limited disease in the proximal femur, whereas its tendency to progress is restricted to a minority of cases, and long-term outcome is usually satisfactory, regardless of treatment, in non-progressive cases. (3) The profile of tibial disease, both in MFD and in PFD, is markedly different from that of femoral disease. (4) As expected, MAS patients have the most extensive disease and the most complicated course, regularly experience multiple fractures, and require adequate surgical treatment. It appears that conservative treatment of femoral fracture, or curettage and cancellous bone grafting, or fixation with screws and plates are not indicated for the treatment of femoral fractures in these patients and should all be discouraged. Internal fixation with intramedullary nails provides stabilization of extensively affected bones, and prevents further fractures and major deformities, and thus providing a better option both for acute and elective surgery in patients with extensive involvement of the femur or of other limb long bones. (5) Evaluation of patients with FD at orthopedic centers should include, but rarely does, a thorough evaluation of endocrine profile and phosphate metabolism, and proper pathological and radiographic assessment.