Polymethyl methacrylate extrusion through a small tibial defect occurred during revision of a long-stemmed total knee arthroplasty. It caused necrosis and ulceration of the overlying skin. Resection of the protruding cement, debridement of the ulcer, and primary closure effected a cure. This is the first report of cement-induced skin necrosis and first report of tibial cement extrusion during revision of a total knee arthroplasty. Subcutaneous cement extrusion should be considered in the differential diagnosis of pretibial ulcers following total knee arthroplasty with cemented stems.