The technique of arthroscopic surgery for the discoid lateral meniscus is very difficult because there is not enough space for arthroscopic operating instrument. As arthroscopic technique has been developing, the symptomatic discoid lateral meniscus become to be treated with arthroscopic total, partial, subtotal meniscectomy and repair, However it is very difficult to choose appropriate arthroscopic procedure. The purpose of this presentation is to choose appropriat,e arthroscopic procedure according to torn shape of discoid meniscus and to demonstrate the arthroscopic surgical technique. One hundred twenty three discoid menisci in one hundred seventeen patients were confirmed by arthroscopy from October 1982 to November 1989. Of these, sixty-four discoid menisci were treated with arthroscopic total meniscetomy, twenty-five with arthroscopic partial meniscectomy, ten with arthroscopic subtotal meniscectomy and ten with arthroscopic repair. However fourteen discoid menisci without tear did not undergo surgical treatment. The shapes of tear were classified into six types:peripheral tear, longitudinal tear, transverse tear, undersurface tear, horizontal tear, multiple tear, The peripheral tear was the most common shape of tear. Eighty percent of multiple tear had tears on two planes (combined longitudinal and horizontal tear). Arthroscopic total meniscectomy is indicated when the symptomatic discoid meniscus has peripheral tear with intrameniscal lesion, horizontal tear or multiple tear. The technique of arthroscopic total excision in one-piece is preferred to piece-by-piece excision. Arthroscopic partial meniscectomy is indicated in the discoid meniscus with longitudinal tear at substance or transverse tear. Five out of twenty-five discoid menisci treated with partial meniscectomy were needed second arthroscopic total meniscectomy due to pain and click. Arthroscopic subtotal meniscectomy is indicated in longitudinal tear occurred at near periphery. Arthroscopic repair and reshaping is indicated in peripheral tear with intact meniscal substance. Repair and reshaping is expected the best treatment for discoid meniscus to prevent degenerative arthritis following total meniscectomy. Discoid meniscus which has no tear or is incidentaly found should be treated with conservative method. As conclusion, all symptomatic discoid meniscus can be treated with arthroscopic procedure. It is very helpful to choose arthroscopic total, partial, subtotal, or repair according to shape of tear.