Avascular necrosis of bone (osteonecrosis) that is atraumatic is most frequently associated with corticosteroid excess or alcoholism and usually involves the femoral head. We report a case of multifocal avascular necrosis in a 38-year-old woman with autoimmune Addison's disease taking corticosteroid replacement therapy. The onset of joint symptoms occurred 6 months after a pregnancy complicated by acute fatty liver and disseminated intravascular coagulation. Although both knees and ankles were involved, an unusual feature is that the hips were spared.As illustrated in this patient, avascular necrosis is frequently misdiagnosed in cases of joint pain of acute onset and may occur in the context of physiologic replacement doses of corticosteroids. Etiologic factors can precede the onset of symptoms and the diagnosis by several months.