To detect and prognosticate osteonecrosis of the femoral head in the preradiographic stage, 60 patients with systemic lupus erythematosus who had normal hip radiology were followed prospectively for a mean period of 5 years (range, 3-7 years) using magnetic resonance imaging (MRI). The first MRI scans showed a low intensity band in the femoral head of normal fat intensity on T1 weighted images in 16 hips of 9 patients. The MRI findings were used to classify the lesions into three categories. Type A (six hips): the lesions occupied the medial one third or less of the weight bearing portion. Type B (two hips): the lesions occupied the medial two thirds or less of the weight bearing portion. Type C (eight hips): the lesions occupied more than the medial two thirds of the weight bearing portion. At the final followup, all of the Type A and one of the Type B hips were classified as being in Stage 1, and one Type B and two Type C hips had progressed to Stage 2. The MRI appearance of six Type C hips had changed from a band to an inhomogeneous pattern with the femoral head progressing to collapse on radiographs 2-5 years after the diagnosis of systemic lupus erythematosus. The remaining hips, which had been classified as normal at the first MRI, maintained a normal appearance, except for one hip that developed a Type A lesion. The presence of a low intensity band on T1 weighted images was an early specific finding of osteonecrosis of the femoral head, and extensive lesions demarcated by band images signified a poorer prognosis in systemic lupus erythematosus patients. If no MRI abnormalities appeared after 1 year of the startup treatment for systemic lupus erythematosus, there was little risk of femoral head collapse based on the subsequent clinical course of the patients followed in the current study.