Multiple pathophysiologies for osteonecrosis have been postulated and various associated risk factors defined for this disease. However, the pathologic findings of the end stage disease are thought to be similar in all patients. To the author's knowledge, there are no data in the literature comparing the pathologic characteristics of osteonecrosis in a quantitative manner between groups of patients with different associated risk factors. The current study examined the pathologic features of core decompression specimens from the femoral head in a group of patients with osteonecrosis associated with corticosteroid therapy and compared them with specimens from patients with osteonecrosis with no history of corticosteroid therapy. The study group comprised 65 patients (96 hips); 45 patients (68 hips) in the corticosteroid group and 20 patients (28 hips) in the noncorticosteroid group. In the corticosteroid group, 65% of dead bone was identified histologically (44 of 68) as compared with 46% (13 of 28) in the noncorticosteroid group. Specimens staged according to the histologic grading system of Arlet and Durroux revealed the corticosteroid group had a higher incidence of late stage lesions than did the noncorticosteroid group. This was found even though the two groups had similar radiographic staging distribution. The hips in patients who used alcohol were comparable pathologically to the hips in patients who used corticosteroids. This study emphasizes that the histologic features of necrosis and repair are similar in corticosteroid and noncorticosteroid osteonecrosis. However, there were differences in the distribution of viable bone and pathologic stage of the lesions in the two groups, suggesting a more rapid evolution of changes in the corticosteroid group.