During a 1978 study of adult arrestees, it was discovered that residency is not a coded variable for records compiled by the San Francisco Police Department computer system. Therefore, the percentage of arrestees who are city residents was not known. Such a statistic can be useful in determining city arrest rates, calculating cost-benefit ratios, projecting future offender populations, and assessing needs and costs of social service and treatment projects. Therefore, this study was developed to collect residency information, which was gathered manually form arrest cards. The sample was selected by choosing 10 arrest cards from 1 day per month for each month from January 1977 through April 1980. In addition to residency, variables collected included sex, address location, and type of offense charged. Data analysis revealed that approximately 74 percent of those arrested on processable offenses (those that require a criminal history record to be kept on the arrestee) and 71 percent of those arrested on minor, nonprocessable charges are city residents. The second most common residency for processable offenders was within a Bay Area county other than San Francisco (16.5 percent), while nonprocessable offenders who lived in a Bay Area county accounted for 9.4 percent. There appeared to be no important differences in residency according to sex of the offender. Four tables and four footnotes are included, and a flow chart and data collection form are appended.