During 1980, American prison populations rose at their fastest rate in 3 years. On January 1, 1981, State and Federal prisons housed 320,583 adults, an increase of over 4 percent from January 1, 1980. Only seven jurisdictions registered declines due to community alternatives programming. Texas showed the largest increase in number of prisoners, while Rhode Island had the largest percentage increase -25 percent. Causes include harsh new laws, the rising violent crime rate, and the effects of the postwar baby boom. The large increase has caused overcrowding and backlogs in local jails. Louisiana has the most serious backlog problem, with the number of prisoners backed up in local jails nearly 3 times higher than in 1980. Other problems caused by the increases are a lack of adequate work programs, insufficient housing, and funding shortages. In addition to increases in the number of new inmates entering prison, fewer inmates are being released due to indeterminant sentencing and conservative parole practices. With Federal emphasis on white-collar crime, fewer new inmates are being received and stays are shorter. Federal commitments for robbery and narcotics now form a higher proportion of the population, mainly due to stricter holdover practices. Tabular data are included.