Osteonecrosis of the femoral head frequently occurs in a young population (mean age, approximately 35 years) and may lead to disabling arthritis requiring hip arthroplasty surgery. This disease is compounded when it has concurrent involvement of other joints. Multifocal osteonecrosis is defined as disease involving three or more anatomic sites. The purpose of this study was to review the demographic, clinical, radiographic staging patterns, and treatment options in patients with multifocal osteonecrosis to facilitate earlier diagnosis and optimize treatment. Twenty-one centers participated by submitting completed data forms on patients under their care after review of their databases. One hundred one patients were identified. Patient demographics, associated diseases, corticosteroids and other medications used, presenting joints, and symptomatology were evaluated. Radiographs and magnetic resonance imaging scans or both were used to diagnose and stage osteonecrotic lesions. Ninety-two of the 101 (91%) patients had a history of corticosteroid therapy. Twelve patients (of 14 tested) were found to have a coagulation disorder. All 101 patients had femoral head involvement. Osteonecrosis also was seen in the knee (96%), shoulder (80%), ankle (44%), and seven other sites. Overall, 631 joints were involved (6.2 lesions per patient). Bilaterality was common: hips, 98%; knees, 86%; and shoulders, 83%. Most lesions (69%) were in a precollapse stage at the time the patients presented for treatment. In eleven patients, the knee was the sole presenting symptomatic joint, and the shoulder and ankle were the sole presenting symptomatic joints in five and four patients, respectively. An improved understanding of the epidemiology, pathogenesis, and etiology of multifocal osteonecrosis will facilitate the diagnosis and treatment of this disease. In patients with osteonecrosis of the hip, all symptomatic joints should be evaluated with radiographs. In patients with osteonecrosis presumably not involving the femoral head, the patient's femoral heads should be evaluated radiographically, regardless of whether the hips are symptomatic.