Magnetic resonance imaging (MRI) findings of 23 patients (13 females, 10 males; 45 knees) with diastrophic dysplasia were examined. The age of the patients ranged from 5 to 40 years (mean 20.5 years). T1- and T2-weighted MR images were obtained. MRI revealed degenerative changes in the articular cartilage of the knees from age 6 years. The subchondral bone of the distal femur was often fragmented, and cartilaginous intrusions from the growth plate into the metaphysis were noted. Menisci developed abnormally. In 43 (96%) of the knees studied, the anterior cruciate ligament was either thinned or rudimentary, or could not be detected. The posterior cruciate ligament was affected in 40 (89%) knees but was at least rudimentary in all patients. In contrast, the patellar tendon was thick and short and the patella was in an inferior position The patella showed bony fragmentation in 32 (71%) knees. The pathologic changes in all joint compartments increased with age, reflecting early degeneration of the knee in this disease.