The femoral heads of 38 normal and 20 abnormal patients were evaluated using magnetic resonance imaging (MRI). The normal femoral head is surrounded by a thin, sharply defined, low-intensity cortex. The medullary cavity has a strong signal intensity in all imaging sequences due to the large content of marrow fat and hematopoietic cells. Crossing the high-intensity marrow is a thin, curvilinear, transverse, low-intensity line representing the physis and a broad, vertically oriented, low-intensity band resulting from the prominent central weight-bearing trabeculae. Anatomic structures can be identified on all scanning sequences if the examinations are technically satisfactory, although images with the best clarity and detail are obtained by using short echo times. MRI of patients with ischemic necrosis revealed areas of low intensity in the femoral heads. The abnormal areas may take the form of homogeneous regions of decreased signal intensity, inhomogeneous areas of low intensity, bands of low intensity, or rings of low intensity with higher signal intensity centrally. No correlation was found among the specific MRI patterns, the stage of the disease, the radiographic appearance, or the radionuclide bone scan findings. MRI was abnormal in all cases where the radiographs or the scintigraphs (or both) were abnormal. MRI also was abnormal in several cases where either radiographs or scintigraphs produced false-negative results.