Prosthetic arthroplasties are performed frequently in arthritic patients. The usual causes of prosthetic failures are loosening, infection, subluxation, or fracture. A 65-year-old man with total knee arthroplasty illustrates the complication of prosthetic synovitis developing 5 years after metal-polyethylene arthroplasty. Double contrast arthrography revealed nodular synovial filling defects. Arthrotomy and hematoxylin-and-eosin-stained histological sections of the synovium showed nonpigmented villonodular synovitis (VS). Giant cells and polyethylene particles were observed by polarized light within the synovium.