We studied indium-111-labeled immunoglobulin G (In-111-IgG) scintigraphy for evaluation of total hip and knee arthroplasty infection in 100 patients (102 arthroplasties) where infection was suspected (85 total hip and 17 total knee replacements, 23 of which proved to be infected, all but 2 late infections). The sensitivity of In-111-IgG scintigraphy for infection was 1.0, for hip and knee arthroplasties the specificities were 0.8 and 0.5, respectively. False-positive results for infection occurred in cementless total hip arthroplasties up to 14 months after implantation. Aseptic inflammation due to formation of ectopic ossification and foreign-body response, following wear of the polyethylene socket, was responsible for false-positive results. The images should be read in conjunction with radiographs, which reduces the rate of false-positive results. In-111-IgG is a highly sensitive and fairly specific tool for detecting of late infection of total hip and total knee arthroplasties.