In a 10-year prospective study, we were able to examine 93 children with 109 hips suffering from Perthes' disease and 6 hips with Meyer's dysplasia epiphysealis by magnetic resonance imaging (MRI) follow-up studies. Routine imaging was done by coronary T1- and T2-enhanced sequences and sagittal T1-enhanced sequences. In total of 400 MR images, the following criteria were evaluated: staging of the disease according to MRI signal changes, extent of the necrosis, prognostic criteria, differential diagnosis of Meyer's dysplasia epiphysealis, and proposals for therapy. Typical signal changes in MRI could be shown following the radiological stages of Perthes' disease. A new staging based on MRI criteria was proposed, which further differentiated the radiological stages I and II: the extent of necrosis could already be predicted exactly in stage I, but did not correlate with the Catterall classification. Therefore, a new method of classification based on MRI distinguishing five different types was defined. We then evaluated the Catterall head-at-risk-signs to see if they had a typical correlation in MRI and also defined risk signs according to MRI criteria. Cartilage thickening proved to be a correlation for lateralization of the epiphysis, and we were also able to demonstrate that deformation of the epiphysis took place early in the course of the disease, i.e., in MRI stage Ib or IIa. Consequently, standards for therapy based on MRI criteria were established. In a second prospective study, we evaluated MRI examinations of 20 children with slipped capital femoral epiphysis. We were able to define typical MRI signal changes for epiphysiolysis in T1- and T2-enhanced images. We also examined the contralateral hips and tried to distinguish an imminent epiphysiolysis from an unaffected hip. Coronary fat-suppressed sequences proved to be the most sensitive. As yet we cannot exactly differentiate the importance of the various signal changes for imminent epiphysiolysis due to the relatively small number of attended patients. A larger number of examinations still have to be done.