Between 1981 and 1986, synovectomy was performed arthroscopically at Düsseldorf University Orthopedic Clinic on 59 knee joints of 56 patients without opening the joint. Of these, 43 patients, i.e., 45 knee joints, were followed up on average 2.7 years postoperatively. In the author's experience arthroscopic-surgical synovectomy puts less strain on the patient. The risk of damaging cutaneous nerve branches is low, neuromuscular joint control is preserved, and no fibroarthrosis occurs. All the compartments of the knee joint - including, in particular, the posterior ones - are accessible from a few stab incisions. Since traumatization is minimal there is less postoperative pain than with the conventional method so that as a rule rehabilitation presents no problems, especially in the first six postoperative weeks. The indication threshold for arthroscopic synovectomy is lower than for conventional synovectomy, thus facilitating the decision to perform synovectomy early. In the event of recurrence the pathologic synovialis can once again be excised from the same approaches.