Eighty Nigerian children (mean age = 8.8 years) with rheumatic heart disease (RHD) were studied prospectively. The initial acute rheumatic fever (ARF) was recognized in 34 of them (42%) while 18 patients (23%) had recurrent ARF. 76 patients (95%) had mitral incompetence, either alone or in combination with other lesions. Symptomatic mitral stenosis was present in 21 patients (26%), occurred early in life, and appeared to be causally related to recurrent ARF and intense host reactions. Aortic and tricuspid valve diseases were uncommon and pulmonary valve disease was rare. 94% of the patients presented in heart failure, and, 4 years after, 20% of those re-examined had improved, 32% remained about the same, and 48% had deteriorated. The high cumulative mortality at 6 years (20%) was attributable to heart failure and subacute bacterial endocarditis. We suggest that in developing countries, all episodes of pharyngitis in children susceptible to ARF should be treated with penicillin, the only exception being pharyngitis associated with definite viral illnesses like measles.