Arthroscopy of the knee is playing an increasingly important role in the treatment of the knee disorders. However, becuase of the invasive nature of arthroscopy, much interest has recently been shown in MRI. In fact, some knee disorders may be better evaluated by MRI than by arthroscopy. The purpose of this study is to determine the accuracy of MRI and discuss s series of case examples in which MRI is equal to or superior to arthroscopy. Between May 1989 and December 1990, 58 patients with possible knee pathology underwent MRI of the affected knee before arthroscopy. The average age of patients was 24 years, with an age range from 12 to 50 years. MR studies were performed on a Hitachi 0.2 T permanent magnet type, and a Solenoid type coil was used. The MRI results were correlated with arthroscopic finding in 51 cases with internally deranged knees. Our results of accuracy of medial and lateral meniscus was similar to findings in other reports in the literature. But accuracy of anterior cruciste ligament was lower than other reports. Some knee disorders we studied were more useful than arthroscopy or can be complementary to arthroscopy. From the above result, authors concluded that MRI has a high accuracy in internally deranged knees, and is more useful than arthroscopy, or can be complementary to arthroscopy for diagnosing and treating xomd disorders of the knee.