BACKGROUND The reduction in US stroke mortality has been attributed to declining stroke incidence. However, evidence is accumulating of a trend in declining stroke severity. METHODS We examined secular trends in stroke incidence, prevalence, and fatality in Framingham Study subjects aged 55-64 years in three successive decades beginning in 1953, 1963, and 1973. RESULTS No significant decline in overall stroke and transient ischemic attack incidence or prevalence occurred. In women, but not men, incidence of completed ischemic stroke declined significantly. Stroke severity, however, decreased significantly over time. Stroke with severe neurological deficit decreased in later decades, with a fall in rates of severe stroke cases in which patients were unconscious on admission to the hospital. There was no substantial change in the case mix of infarcts and hemorrhages and no decline in hemorrhage to account for the decline in severity. The proportion of isolated transient ischemic attacks increased significantly over the 30 years studied, yielding an apparent and significant decline in case-fatality rates in men only. CONCLUSIONS Secular trends in stroke incidence and fatality did not follow a clear or definite pattern of decline. While a significant decline in stroke severity occurred over three decades, incidence of infarction fell only in women. The decline in total case fatality rates occurred only in men and resulted largely from an increased incidence of isolated transient ischemic attacks. The severity of completed stroke was significantly lower in the later decades under study.