This study compared rheumatic heart disease prevalence data obtained from standard clinical screening with echocardiographic confirmation of suspected cases and from systematic screening with echocardiography screening, in populations of children aged 6 to 17 years in Cambodia and Mozambique. Clinical evidence of rheumatic heart disease confirmed by echocardiography was found in 8 of 3677 children in Cambodia and 5 of 2170 children in Mozambique; corresponding prevalence rates were 2.2 cases per 1000 and 2.3 cases per 1000, respectively. However, echocardiographic screening revealed 79 cases of rheumatic heart disease in Cambodia and 66 cases in Mozambique, corresponding to prevalence rates of 21.5 cases per 1000 and 30.4 cases per 1000, respectively. In the majority of cases, the mitral valve was involved (87.3% in Cambodia and 98.4% in Mozambique). In view of the fact that rheumatic heart disease frequently has devastating clinical consequences and secondary prevention may be effective after accurate identification of early cases, these results have important public health implications, the study concludes.