The data forming the basis of the indicator came from annual inmate censuses conducted by the Bureau of Justice Statistics (BJS) and from nationwide surveys conducted in January 1974 and October 1979. Both surveys involved interviews with large samples of inmates of State prisons. Prevalence of imprisonment was calculated for six population segments: white males, black males, males of all other races, white females, black females, and females of all other races. About 1 percent of the Nation's adult population was found to be imprisoned on any given day. At 1973 imprisonment levels, a person born in the United States today was estimated to have a 1.3 to 2.1 percent lifetime chance of serving a sentence in an adult State prison. Males were about 26 times more likely than females to be in prison on any given day and almost 15 times more likely to serve a prison term in their lifetimes. The prevalence of imprisonment was substantially higher for blacks than for whites. First-time prisoners had a 29 to 38 percent chance of returning to prison. The data indicated that a substantial proportion of the Nation's population experiences incarceration, although the causes are unknown. The results provide a benchmark against which future correctional alternatives can be evaluated. Seven data tables, 3 appendix tables, 41 footnotes, and a list of BJS reports are supplied.