Forty patients were re-examined between 6 months and 15 years (mean 4 years) after excision of a popliteal cyst. Forty-six operations had been performed, including one bilateral cyst and five recurrent cysts. The history was reviewed with respect to the preoperative symptoms, clinical and roentgenological signs, the operative and histopathological findings and the postoperative course. Fifteen operations were followed by wound healing complications or tense swelling of the calf simulating deep venous thrombosis. At clinical follow-up a reccurent cyst was found in 63 per cent of the knees. A simplified follow-up arthrography was performed in all knees, and revealed a cyst-like cavity in all but one knee. The majority of the recurrent cysts displayed irregularities of the wall that had not been seen in the preoperative arthrograms. Despite this high rate of recurrence most of the patients had fewer symptoms from the popliteal space at the time of follow-up than before the operation. as associated knee disorders were present in the majority of patients, popliteal cysts (Baker's cysts) should be regarded and, if possible, treated as secondary to the basic pathological condition of the joint. Only if the knee disorder is not curable and if the symptoms from the popliteal region are troublesome should excision of the cyst and tight closure of the communication with the joint be considered.