More than 3 million persons in the United States over the age of 60 have isolated systolic hypertension. They face an excess risk (2-3 fold) of stroke, other cardiovascular disease and death. Population-based data show that the prevalence rises from approximately 8 percent in the age group 60-69 years to approximately 20 percent over the age of 80. Based on available data, an annual stroke rate of 2.0 percent has been estimated in this population. The full-scale clinical trial followed a pilot study conducted from 1980 to 1983. Recruitment in the trial began in March 1985 and was finished in January 1988. Follow-up ended in February 1991. Data analysis continued through October 1996.