Bone single photon emission computed tomography(SPECT) of the knees has been shown to be of diagnostic value for the investigation of intemal derangement of knees(IDK). This study compared bone SPECT and magnetic resonance image(MRI) with arthroscopic findings for the diagnosis of IDK. Fifty patients who had been performed arthroscopy in Seoul National University Hospital from January 1997 to September 1997 were studied with both the modalities preoperatively. There were 38 meniscal injuries, 26 cruciate ligament injuries and 8 cases of patellofemoral joint problems. In view of SPECT, the most remarkable results were from meniscal tears. In meniscal tears, the diagnostic values of SPECT were 89.5% of sensitivity, 66.7% of specificity, 84% of diagnostic accuracy, which were comparable to those of MRI, 97.4%, 91.7% and 96%, respectively. But SPECT showed inferior diagnostic values in cruciate ligament injuries. For anterior knee pain, SPECT was more sensitive than MRI for the detection of pathology. And for functionally related cases, such as ACL impingement to intercondylar notch, SPECT was far more valuable than MRI. Bone SPECT will not provide the anatomical detail of MRI but seems to be a useful tool for the detection of wide range of knee disorders including IDK. Further research is justified to investigate the precise role of bone SPECT in clinical practice and its value in relation to MRI.