Prosthetic replacement surgery for hip, knee, shoulder, and elbow joints has become commonplace due to the great success of these procedures in restoring function to persons disabled by arthritis. One of the most feared complications is prosthetic joint infection, which is associated with significant morbidity and health care costs. The pathogenesis of prosthetic joint infections is influenced by microorganisms growing in biofilms, making these infections difficult to diagnose and eradicate. Low-grade infections are often manifest as early loosening with or without pain. They are therefore difficult to distinguish from aseptic failure. For an accurate diagnosis of prosthetic joint infections, a combination of preoperative and intraciperative tests is usually needed. Underlying rheumatologic disease can lead to periprosthetic inflammatory changes in tissue. Therefore, only the culture of the microorganism is definitive proof of infection. Successful treatment requires long-term antimicrobial therapy, ideally with an agent acting on adhering stationary-phase microorganisms, combined with an adequate surgical procedure. In this article, the epidemiology, pathogenesis, diagnosis and treatment of prosthetic joint infections are reviewed. We focus on difficult diagnostic aspects in the context of underlying rheumatologic disease.