The authors describe three patients in whom septic arthritis of the sternoclavicular joint (SCJ) occurred, drug addiction and human immunodeficiency virus (HIV) infection representing the predisposing conditions. Infectious arthritis is well known in intravenous drug users, but it is rare in HIV positive patients, who are prone to bacterial infections from usual or unusual microorganisms. In one case, staphylococcus aureus methicillin sensitive was responsible for septic arthritis. In another case, SCJ infection was associated with pneumonitis.