Recent technological advances have made magnetic resonance images (MR) of the knee a clinical reality. MR is rapidly replacing the conventional arthrography as the imaging modality of choice of the knee joints. To evaluate the diagnostic accuracy of MR in the internal derangement of the knee, MR findings of 244 menisci and 488 ligaments of 122 knees were correlated with those of subsequent arthroscopy or surgery in all cases. The sensitivity, specificity, and accuracy of MR diagnosis for the medial meniscus were 87%, 93%, 91%, for the lateral meniscus 91%, 95%, 93%, for the anterior cruciate ligament 80%, 97%, 92%, for the posteriior cruciate ligamant 73%, 99%, 97%, for the medial collateral ligament 67%, 100%, 99%, for the lateral collateral ligament 100%, 100%, and 100%. These results imply that MR is an excellent diagnostic modality in the preoperative evaluation of clinically suspected internal derangement of the knee.