Sixty four children who presented with the initial attack of acute rheumatic fever and maintained continuous regular secondary prophylaxis, were followed up prospectively for 12.3 years (an observation period of 775 patient-years). The prevalence rate of rheumatic heart disease in the 29 children who had carditis in the initial attack and in the 35 children who had no carditis initially was 49 vs 0%, respectively. The overall prevalence rate of rheumatic heart disease was 20%. Mitral incompetence developed in 11 patients (17%), aortic incompetence in 2 (3%) and mitral stenosis in 2 (3%). None of the patients developed aortic stenosis. Two recurrences developed with a recurrence rate of 0.003 per patient per year. One patient needed cardiac surgery and there was no mortality. These data strongly suggest that continuous regular secondary prophylaxis can prevent or significantly reduce the development of mitral and aortic valve stenosis, the prevalence rate of rheumatic heart disease and mortality.