Arthrography is a widely used procedure for accurate diagnosis of the internal derangement of knee joint, but there is disagreement regarding its relative accuracy. In order to evaluate diagnostic accuracy of knee arthrography, the authors examined 101 cases which had undergone through arthrography, arthroscopy and/or arthrotomy out of 96 patients. The results of this study were as follows ; 1. The accuracy rate of clinical diagnosis in I.D.K was 65.3%. 2. The accuracy rate of arthrographic diagnosis in I.D.K was 68.3%. 3. The combined accuracy rate of clinical and arthrographic diagnosis in I.D.K was 97.2%. 4. The diagnostic accuracy rate of arthrographic diagnosis in meniscal lesion was 79.3% and was 80.0% for medial meniscus, 62.5% for lateral meniscus and 84.4% for lateral discoid meniscus respectively. 5. Arthrography is a good auxiliary method for detection of the meniscal lesion but not suitable for other lesions in the knee joint.