We studied the bone histology by histomorphometric methods in transiliac bone-biopsy specimens from seventy-seven adult patients with aseptic osteonecrosis and normal kidney function. The trabecular bone volume, trabecular osteoid volume, trabecular osteoid surfaces, thickness index of osteoid seams, total resorption surfaces, calcification rate, tetracycline-labeled surfaces, and bone-formation rate at the basic multicellular unit level and at the tissue level were determined. Histological evidence of osteomalacia was found in nine patients, of whom four were alcoholics. In the remaining sixty-eight patients--fifteen treated with corticosteroids, twenty-nine alcoholics, and twenty-four who did not have any detectable etiological factor--a common histomorphometric profile was found. This consisted morphologically of a reduction in trabecular bone volume and in the thickness of osteoid seams, and dynamically of a reduction in calcification rate and in total labeled surfaces. All of these changes suggested a marked decrease in osteoblastic appositional rate and in bone-formation rate at the cell and tissue levels. This could induce a healing defect of microfractures and thus facilitate subchondral fractures. Clinical Relevance: This histological study indicated that non-apparent bone disease--either osteoporosis or osteomalacia--may underlie aseptic osteonecrosis in almost all patients, and be found even when blood and urinary biochemical parameters, usually reflecting bone-remodeling, are normal. An iliac-crest bone biopsy with static and dynamic histomorphometric study is the appropriate method for detecting these abnormalities. These results are of importance for understanding the pathophysiological mechanisms underlying osteonecrosis as well as its prevention and treatment.