Pseudoaneurysms of the popliteal artery after total knee arthroplasty are rare. Although many possible explanations are proposed in the literature, no intimate mechanism of injury to the artery is previously described. We report on a case of popliteal pseudoaneurysm after a total knee arthroplasty that presented clinically on the second postoperative day. Open vascular surgery with resection of the pseudoaneurysm and end-to-end bypass of contralateral saphena vein graft was successfully performed. At the time of the surgery, a hole was clearly identified on the anterior wall of the popliteal artery due to a perforation with a pin used during the knee arthroplasty. The patient had no further complications.