The case of a recurrent hemarthrosis of a total knee arthroplasty after the sixth postoperative month is described. Because of disabling pain, the patient underwent an explorative arthrotomy 18 months after implantation of the total knee arthroplasty. A hypertrophied vascular mass of synovium was discovered in the lateral gutter and excised with an associated synovectomy. Since the arthrotomy, the hemarthrosis has not recurred. Therefore, in cases of recurrent hemarthrosis of a total knee arthroplasty that becomes disabling, exploration by arthrotomy should be considered.