During the period from January 1990 to December 1998 65 patients were operated upon for a Baker's cyst. 41 patients (43 operations) were subjected to a clinical and sonographical follow-up examination and interrogation. In 11 cases, the cysts were merely removed, while an open synovectomy was carried out four times (rheumatics) in addition to the removal of the cysts, and arthroscopy with exstirpation was performed in 28 cases. The total recurrence rate was 14 % (6/43). Any significant differences between the groups were not found (p = 0.291). The overall complication rate was 18.6 %. In case of recurrence, the clinical results were significantly worse (p = 0.036). Apart from technical aspects of operation, the not quantifiable correlation between grade of chondromalacia and the formation of effusions following joint degeneration has to be discussed as a cause for recurrences. If both interventions are carried out in one course, there is no increased operative risk. Especially in cases with intraarticular pathological symptoms arthroscopy should precede each cyst exstirpation. With regard to the frequency of recurrence, the patients' expectation should be preoperatively objectified.