Osteochondrosis dissecans (OCD) is a lesion that characteristically affects the articular cartilage and subchondral bone with the potential of fragmentation and separation. Exact assessment of cartilaginous and subchondral bony changes is mandatory for the planning of adequate treatment. Therefore, we examined 25 knees using spin echo (SE) and gradient echo (GE) sequences on a 1.5 T superconducting unit prior to and following intraarticular administration of 40 ml of a 2 mmol/L Gd-DTPA solution (MR arthrography). For evaluation (staging) a modified Clanton and DeLee scheme was employed. Verification by arthroscopy or arthrotomy was available in 24 cases. A correct diagnosis of OCD with regard to its type prior to intraarticular injection of Gd-DTPA was possible in 39.3% using T1-weighted SE sequences and in 57.4% on GE sequences. After intraarticular administration of Gd-DTPA, the rate of correct diagnoses improved to 92.9% on T1-weighted SE sequences and 100% on GE sequences. Magnetic resonance arthrography appears to be helpful for the exact assessment of the articular cartilage overlying OCD lesions as well as for the differentiation between partial and complete separation of cartilaginous or osteocartilaginous fragmentations.