The acromioclavicular joint is rarely the site of septic arthritis. We conducted a retrospective review at our rheumatology department, which identified five cases within the last 6years. All five patients were males, and their mean age was 63years. Risk factors were consistently identified and included intravenous substance abuse, prior joint disease, a recent history of intraarticular injections, and a remote history of surgery. Joint aspiration was performed in all five patients and provided the organism in two patients. Blood cultures recovered Staphylococcus aureus in three patients, a coagulase-negative Staphylococcus in one patient, and no organism in one patient. Ultrasonography and/or magnetic resonance imaging established the early diagnosis in four patients and ruled out concomitant involvement of the glenohumeral joint. Only about 20 cases of septic arthritis of the acromioclavicular joint have been reported to date. This rare infection must be diagnosed rapidly to prevent joint destruction. The treatment is that usually recommended for septic arthritis.