In 1972 we conducted a survey of 12,050 urban Black schoolchildren and detected 168 (prevalence rate of 14 per 1,000) with a non-ejection systolic click (NESC), a late systolic murmur, or both. The etiology of the mitral valve abnormality was unknown but we considered that a significant proportion might have early rheumatic heart disease. The auscultatory features four years later of 139 of the original 168 subjects as well as those of 139 age- and sex-matched controls are presented in this study. No cardiac abnormality was detected in as many as 55 of the subjects. Five children now had pansystolic murmurs but the mitral regurgitation was assessed as mild in four. Twenty-five (17.9 per cent) of the controls, 23 of whom had NESCs, had auscultatory features compatible with mitral valve prolapse. These findings do not support our earlier suggestion that a large number of the 1972 subjects have mild rheumatic heart disease. The results are in accord with other studies which have indicated that auscultatory features compatible with mitral valve prolapse are common in "normals" and also that the prognosis of the specific "billowing mitral leaflet syndrome" is generally benign.