PURPOSE: We wanted to evaluate the clinical characteristics of patients with multifocal osteonecrosis. MATERIALS AND METHODS: When two or more anatomic sites were affected by osteonecrosis, this was defined as multifocal osteonecrosis. We retrospectively reviewed the cases of multiple osteonecrosis that were diagnosed between January 1982 and December 2003, and we analyzed such clinical characteristics as the risk factors, the involved sites and the symptoms. RESULTS: Thirty-three of 1740 patients (2%) with multifocal osteonecrosis were found. They were 16 men and 17 women with a mean age of 48.7 years (range: 28 to 74). The associated factors included systemic lupus erythematosus (6 patients), aplastic anemia (2 patients), malignancy (2 patients), multiple sclerosis (2 patients), idiopathic pulmonary fibrosis (1 patient), Caisson's disease (1 patient), idiopathic (9 patients) and alcohol abuse (6 patients). Seventeen of 33 patients (52%) had a history of corticosteroid therapy. The involved sites included 33 femoral heads, 22 femoral and tibial condyles, 13 humeral heads, 4 talar bodies and 1 scaphoid. In total, 132 sites were involved (4.0 per patients). CONCLUSION: Chronic steroid therapy affected the high incidence of multifocal osteonecrosis. Therefore, further studies that would include bone scans are needed for patients who undergo steroid therapy, and especially when these patients show clinical symptoms.