Twenty-two patients (24 hips) with Legg-Perthes disease received 49 magnetic resonance (MRI) scans. The scans and corresponding radiographs were independently evaluated in a blinded fashion to assess the capabilities of, and indications for, MRI in Legg-Perthes disease. Early in the disease process, MRI often more clearly delineated the extent and location of areas of involvement than did plain radiographs. In one patient, MRI failed to indicate necrosis early in the course of the disease, but it was detected on plain radiographs. MRI can also be used to give a rough estimate of sphericity, which in some phases of the disease process is better than plain radiographs. For serially following the disease process through the natural healing course, plain radiographs were as good or better than MRI and considerably less costly.