The prevalence of rheumatic fever and rheumatic heart disease reflects the adequacy of preventive medical care in any given community. In more developed countries, these diseases have become rare, whereas in many developing countries, rheumatic heart disease remains the leading cause of heart disease among children and young adults. Inadequate prevention may lead to strikingly disparate trends within the same country. In South Africa, for example, the prevalence of rheumatic fever has decreased substantially among the white minority as it has in other developed countries, whereas among the schoolchildren of Soweto, who live in the large black ghettos near Johannesburg, the reported prevalence in 1996 was 6· 9 per 1000 children, increasing to 20 per 1000 among those aged 12–14 years (grades 7 and 8). 1 Similarly, the point prevalence of rheumatic heart disease in another segregated population, a community of aborigines in Northern Australia, has been reported as 9· 6 per 1000, with a staggering rate of 24 per 1000 in one large rural comunity. 2 High rates of rheumatic heart disease are found in other deprived communities, such as the Samoan children in Hawaii (2· 06 per 1000), Sri Lankans aged 5–19 years (1· 42), and Maori children in Auckland, New Zealand (1· 25). By contrast, rates of rheumatic heart disease in affluent, developed communities are usually about 0· 2–0· 5 per 100 000. 2 In the more developed countries, many young physicians have never seen a patient with rheumatic fever. These physicians treat patients with sore throats almost daily, but do not have any detailed knowledge of the clinical microbiology of the group-A streptococci extant in their community. They find themselves making decisions about whether cephalosporins, rather than penicillin therapy alone, constitute appropriate primary preventive therapy for rheumatic fever, 3 and whether or not antibiotics are necessary for pharyngitis. 4 This seminar emphasises the importance of early diagnosis and reporting of a patient with acute rheumatic fever, because such a patient can introduce into the community strains of group-A streptococci that are capable of causing the disease; these strains are known, appropriately, as rheumatogenic. 5 The detection of a case of acute rheumatic fever in a community should lead to the prompt treatment and prevention of streptococcal pharyngitis by the stringent treatment regimens required for primary prevention of rheumatic fever.