Rheumatic fever is a disease that affects all parts of the body and has a special predilection for involvement of mesenchymal tissue. The onset may occur at any time, but children over the age of 5 and young adults seem to be most often affected. The course of individual cases is unpredictable, and the prognosis is dependent primarily upon the degree of residual heart damage after the acute episode has subsided and upon the prevention of subsequent recurrences. The severity of rheumatic fever seems to have decreased since 1900 with less residual rheumatic heart disease. The incidence of rheumatic fever is also decreasing in the United States, and the fall in mortality rates was documented prior to the advent of antimicrobial agents. However, the frequency of rheumatic fever and the prevalence of rheumatic heart disease remain high in the economically and socially disadvantaged populations. In spite of numerous investigators carrying out clinical research over a number of decades, rheumatic fever continues to tax the diagnostic acumen of physicians caring for children and young adults.