Several problems have made it difficult to obtain adequate data on the prevalence and severity of cardiovascular disease as a health problem among American Indians. The small size, relatively young age, cultural and anthropological diversity and the geographic dispersion of the American Indian population have made it impractical to examine large numbers of subjects for research and vital statistics surveys. Excess mortality among younger Indians from noncardiovascular causes may have obscured the true risk of cardiovascular disease in this population. Definitions of the term 'Indian' are variable in published reports. The denominators from which disease rates were calculated often were based on uncertain estimates of the population at risk. Definitions of disease and methods of its ascertainment have varied in different studies. In addition, health care services available to Indians vary considerably in different geographic areas, and possibly contribute to differences in reported morbidity and mortality.