More than 700 total knee arthroplasties were performed in our Department between 1992-2000. 6 patients developed pain on the postero-medial aspect of the knee, within 1 year of surgery. The pain increased during walking and especially on rising from a chair. All patients were women with good knee motion and good alignment of the implanted prosthesis. We found no signs of low-grade infection. Injection of 1% Xylocaine relieved pain for a short time in all patients. They were all treated with excision of the reflected portion of the semimembranosus tendon which was not cut during the arthroplasty. Pain was completely relieved in 5 cases and improvement occurred in 1.