Acute rheumatic fever (ARF) in 53 adults was characterized by a severe, febrile migratory polyarthritis involving primarily large joints in the lower extremities, with evidence of an antecedent streptococcal infection. Carditis, present in only eight (15%) of the adults, was mild and transient. The characteristic abnormality in laboratory findings was an erythrocyte sedimentation rate (Westergren) greater than 100 mm/hr. Response to high-dose aspirin therapy was prompt and dramatic in all patients. Mild andevanescent abnormalities of both renal function and hepatic function (not aspirin-mediated) were detected in 51% and 64%, respectively. A common disorder in San Antonio, ARF has distinctive symptoms. It can be readily diagnosed and promptly treated. In the adult, it is almost exclusively a syndrome of events severe but transient in the joints, and mild and transient in the heart, kidneys, and liver.