The study found significant gender differences in drug use and associated problem behaviors among the arrestees. Women arrestees were significantly more likely than men arrestees to have used heroin and crack, and the men were significantly more likely to have used cannabis, ecstasy, and cocaine powder. In addition to their greater use of "hard" drugs, women used heroin and crack at a higher rate than men. Women were also more likely than men to report being dependent on these more serious drug types. These findings remained significant even after controlling for other demographic factors such as age, ethnic group, marital status, and employment status. Gender differences were also found in treatment need. Among arrestees who had used drugs in the last 12 months, women were significantly more likely than men to be in treatment or to want treatment. Regarding criminal offending, men were more likely than women to report having committed vehicle offenses, burglary from a nondwelling, and drug dealing. Women were more likely than men to report shoplifting, theft from a person, fraud, and prostitution. Possible explanations for these findings are offered, and implications are drawn for future research and drug-related policies. Data were collected in personal interviews with a structured questionnaire, which contained questions on self-reported use of 19 illicit drug types and offending behavior related to 11 income-generating crimes. Arrestees were also asked to provide a urine sample that was analyzed for the presence of cannabis, opiates, cocaine, benzodiazepines, amphetamines, methadone, and alcohol. 11 tables and 44 references