One hundred and twenty-six children with the initial attack of acute rheumatic fever were followed up prospectively for 6 years. Sixty-six children maintained regular secondary prophylaxis (regular group) and 60 were irregular (irregular group). Two recurrences developed in the regular group with a recurrence rate of 0.005/patient/year follow-up, and 71 recurrences developed in the irregular group with a recurrence rate of 0.2/patient/year follow-up. These findings demonstrate the effect of secondary prophylaxis in reducing the frequency of recurrences. The prevalence rate of rheumatic heart disease in children who had carditis in the initial attack was 42% in the regular group vs 70% in the irregular group (p less than 0.05). These findings demonstrate the deleterious effect of recurrences in the evolution of rheumatic heart disease. The prevalence rate of rheumatic heart disease in children who maintained regular secondary prophylaxis, was 42% in those children who had carditis in the initial attack and 6% in those who had no carditis (p less than 0.05). These findings demonstrate the prognostic significance of presence or absence of carditis during the initial attack, in the subsequent evolution of rheumatic heart disease. The prevalence rate of rheumatic heart disease in the 66 children who maintained regular prophylaxis was 23%. Comparison of these data with those of similarly designed studies shows that the evolution of rheumatic heart disease following the initial attack of acute rheumatic fever, seems to behave similarly in the tropics and subtropics as it did in temperate climates.