Pigmented villonodular synovitis is a rare benign tumor. The high rate or recurrence after surgery exposes the risk of non-conservative or non-functional treatment. External irradiation of post-surgical residual disease seems to be useful for the prevention of relapse and conservation with a good functional result. We report a clinical observation of a case with a diffuse type of pigmented villonodular synovitis of the ankle, operated on three times, and then treated by external irradiation. The published results in terms of response and functional prognosis of 14 cases of multi-recurrent villonodular synovitis treated by irradiation seem to confirm this therapeutic option.