Ten definite cases of rheumatic fever occurring under 3 years of age are reported. These represent 0.5% of all initial attacks of rheumatic fever in children 16 years old or less admitted to our hospital between 1939 and 1966. Thus, rheumatic fever in the first few years of life is rare but not nonexistent. Our youngest patient was 19 months old. The predominant manifestations of the disease in the first few years of life were carditis and congestive heart failure, and all but one of the patients had significant mitral regurgitation. Polyarthritis was also a common feature. Elevated antistreptolysin-O titers were demonstrated in all cases in which the test was performed. Therefore, evidence of a preceding streptococcal infection is important in considering this diagnosis, even in children under 3 years of age. The differentiation of rheumatic fever from congenital heart disease, viral myocarditis, and rheumatoid arthritis is dicussed. In our experience, the prognosis for the infant with rheumatic carditis has improved since the introduction of penicillin and corticosteroids.