The precise diagnosis of internal derangement of the knee is difficult, since the signs and symptoms are frequently obscure. For this reason, diagnostic aids have long been sought, and arthrogrphy has been widely used as a means to improve diagnostic accuracy. Recently, post-arthrographic high resolution computed tomogrphy has been added to the diagnostic techniques for the evaluation of the knee. Arthrography and post-arthrographic high resolution computed tomography were carried out in 97 cases of clinically suspicious meniscal tear from January 1986 to October 1987. Among them, 40 cases were confirmed by arthroscopic surgery and following results were obtained. l. Arthorgraphy resulted in a diagnostic accuracy of 92.5% and 72.5% for medial and lateral meniscal lesion. Post-arthrographic high resolution computed tomography resulted in that of 95.0% and 90.0% for each meniscal lesion. 2. 16 cases of them were discoid meniscus. 13 cases(92.5%) were detected by arthrography and 16 cases(100%) by post-arthrographic high resolution computed tomography. 3. The sensitivity of arthrography was proved to be 100% and 65.4% for medial and lateral meniscal lesion, and thst of post-arthrographic high resolution computed tomography to be 100% snd 88.5% for each meniscal lesion. The specificity of arthrography was 90.0 and 85.7% in each meniscal lesion and that of post-arthrographic high resolution computed tomography was 93.3% and 92.9% in each meniscal lesion. 4. Post-arthrogrsphic high resolution computed tomography was proved to show better diagnostic accuracy, and good visualization of the relationship and extent of torn meniscal lesions. The meniscal anatomy that was displayed by high resolution computed tomography more accurately depicted the anatomical findings that were seen at arthroscopy. With this additional information, arthroscopists could plan more appropriate surgical approach.