The methods of treatment of discoid meniscus have been in controversy and there are so many reports which represent different results. We analyzed the results of the 91 knees with discoid menisci of 84 patients who had been treated with arthroscopic partial or total meniscectomy, open partial or total meniscectomy, semi-arthroscopic total menisceetomy form June 1982 to Dec. 1987. The puropse of this paper is to present the indication and prognosis of the each method of treatment. There were 45 cases of male, 46 cases of female, and 10 patients were affected both knee. 2 patients who had served arthroscopic partial meniscectomy were reoperated by arthroscopic total meniscectomy due to recurrence of symptom. We classified the types of tear into 7 classes and observed the clinical characteristics and results. The methods we applied were arthroscopic total meniscectomy 40 cases, semi-arthroscopic total meniscectomy 25 cases, arthroscipic partial meniscectomy 16 cases, open partial meniscectomy 3 cases, open total meniscectomy 2 cases, and conservative treatment after arthroscopic diagnosis 5 cases. The follow up cases were 56, and period of follow up was ranged form 11 months to 5 years and 4 months (av. 2 years and 8 months). The results were followings : l. 71.4% of the patients were placed between 11 years and 30 years old, and there was no sexual difference. 2. 11.9% of the patients were affected bilaterally. 3. The commonest clinical symptom and physical sign was clik (67%) and quadriceps muscle atrophy (48.4%) 4. Diagnostic accuracy of knee arthrogram was 88%, but it could not demonstrate the type of tear. In arthrographic finding, the older the patient, the thinner the meniscus was. 5. The commonest type of tear was type V(34.1%) and it was followed by type II (19.8%). 6. There was no difference between the long term results of arthroscopic and semi-arthroscopic total meniscectomy. 7. The results of total meniscectomy is better than partial meniscectomy.8. The method of treatment should be chosen according to the type of terar, so partial meniscectorny is recommended for type II, IV and total meniscictomy is recommended for type III, IV, V and VI. 9. Less hospitalization, earlier recovery, and better result were obtained by the arthroscopic or semi-arthroscopic total meniscectomy.