A painful and swollen prosthetic joint, accompanied by fever, is considered to be an intra-articular infection until proven otherwise. Acute gout is one of the rare causes of arthritis in a prosthetic joint, and it may be misdiagnosed as an infection, especially when a high leukocyte count is present in the joint fluid. We report a case of crystal-proven, gouty arthritis with a low synovial fluid leukocyte count presenting with pain and swelling in a prosthetic knee and responding to treatment with colchicine and corticosteroids. Physicians taking care of patients with prosthetic joints should be aware that acute gout can occur in an artificial joint and that aspirated prosthetic joint fluid should be routinely screened for crystals independently from the WBC counts obtained.