Accuracy in the assessment of lesion extension, specificity for histologic type and tumour status were reviewed in MRI and CT scans of 27 chondrosarcomas, 18 osteochondromas and 10 enchondromas and compared with the results obtained by plain radiography. No significant differences in the description of the lesion were found in chondrosarcomas and enchondromas between MRI and CT. In osteochondromas cartilage caps smaller than 5 mm and isodense to muscle were missed or not adequately delineated in CT. The specificity for the primary benign and malignant forms was equally high for CT and plain films, while MRI implies a much lower specificity due to the low sensitivity for matrix mineralisations. The criteria for malignant transformation of osteochondromas are visualised to better advantage by MRI. Solid ossified and small unmineralised recurrences of chondrosarcomas are detected by MRI with a higher sensitivity and specificity than by CT.