We studied the prognostic value of MRI in 32 radiographically normal, asymptomatic hips in 25 patients at risk of osteonecrosis from glucocorticoids or alcoholism. The early findings were band-like hypointense zones on spin-echo images. No operations were performed. Life-table survival curves showed that femoral heads in which the hypointense zone traversed the middle portion of the head were most at risk of subsequent segmental collapse.