The duration of rheumatic fever was determined in 1169 admissions. Seventy-six attacks lasted more than 223 days. Six were found to be diagnostic errors 2 had systemic lupus erythematosus, one endocardial fibroelastosis, 2 infectious arthritis, and 2 recurrent rather than "chronic" rheumatic fever. Sixteen had elevated erythrocyte sedimentation rates only, beyond the two hundred twenty-third day of their attack. On follow-up examination of 11, the cardiac status was unchanged or improved, although 4 still had elevated sedimentation rates. Fourteen had chorea only, and a good prognosis. The 40 remaining attacks were severe as well as prolonged. Twenty-one had congestive heart failure; of these, 3 developed auricular fibrillation or further enlargement of the heart, and 12 had other clinical manifestations of rheumatic fever. Nineteen had no congestive heart failure, but did have other clinical manifestations. The frequency of these severe or "true chronic" attacks increased with the number of previous attacks of rheumatic fever and with the presence and severity of heart disease early in the attack. Late post-therapeutic rebounds and spontaneous relapses were more frequent than in un-selected rheumatic fever. Thirteen of these patients have died and typical Aschoff bodies were described in only one of 11 autopsies. Fresh non-bacterial endocarditis was present in 3, and recent pericarditis in another 2. Serial streptococcal antibody determinations failed to show intercurrent streptococcal infections in 27 of these 40 patients. This suggests that the inflammatory rheumatic process can occasionally continue long after a streptococcal infection has subsided.