Data for the inmate population projections and the study of alternatives to incarceration were collected from the automated data system of the Sheriff's Department; other aggregate criminal justice data were obtained from various State agencies; and information was collected from pertinent reports about the adult detention system and from interviews with representatives of county criminal justice and community-based agencies. The findings show that the San Francisco adult detention system has been overburdened for the last several years, and the county's three jails have been operating well over their rated capacities. Large numbers of persons are jailed for relatively minor offenses and for brief periods. Many are in jail because of alcohol and drug abuse, mental health problems, and homelessness. Although the average daily jail populations will likely continue to rise slightly over the next 3 years, under current policies the average jail population should remain stable after 1990. Expanded alternatives to jail and the increased use of community beds are recommended.