Discoid medial meniscus was first reported in l930 by Watson-Jones. Discoid medial menisci are very rarely reported although the presence of discoid lateral menisci are not uncommon. From Jan. 1989 to Dec. 1994, we have experienced five cases who had discoid medial menisci with pain due to substance tear following knee injury in arthroscopy. There were three complete type anct two incomplete type. Out of flve cases, longitudinal tea1 and bucket-handle type tear were two, respectively. The remained one was a compound tear.