Purpose: F-18 FDG (FDG) is reportedly useful for detecting infection. Because the procedure is simple, with results being readily available, this prospective study was undertaken to evaluate the utility of FDG imaging for diagnosing infected joint replacements.Methods: 26 pts, 18 females and 4 males between 37 and 87 years old, with 31 joint replacements were studied. 21 pts had single joint replacement (10 hip, 11 knee); 5 pts had bilateral replacements (1 hip, 4 knee). Imaging was performed on a Hybrid PET system, with measured attenuation correction, one hour after administration of 150 MBq FDG. Increased peri-prosthetic uptake compared to adjacent, presumably normal, activity was interpreted as positive for infection.Results: 11 of 31 prostheses were infected. Sensitivity, specificity, and accuracy of FDG were 100%, 55%, and 71% respectively. The PPV was 55% and the NPV was 100%. Excluding the 5 asymptomatic prostheses in pts with bilateral joint replacements, the sensitivity, specificity, and accuracy were 100%, 47%, and 69% respectively. The PPV was 58% and the NPV was 100%. 4 pts with infected prostheses underwent a total of 6 follow-up studies after treatment. In 1 pt with persistent infection, all 3 follow-up studies were true positive. In the other 3 pts in whom infection had been eradicated, follow-up FDG studies were false positive.Conclusion: FDG imaging is sensitive but not specific; consequently, its role in pts with suspected prosthetic infection is limited to that of a screening test. These data also suggest that this technique is not useful for monitoring response to treatment.