We present three cases of suspected septic arthritis in which the joint fluid was sterile. Subsequently all three patients were diagnosed with established moderate-severe rheumatic heart disease. In retrospect it is likely that the earlier presentations were in fact episodes of acute rheumatic fever but were not recognized as such. These cases underline the importance of acute rheumatic fever as a differential diagnosis of septic arthritis when the joint fluid is sterile, particularly in regions where there are high rates of acute rheumatic fever and rheumatic heart disease.