The data show that, while a significant minority of heroin users have never been arrested, most heroin users have an arrest record; the majority of users with a record were arrested prior to their first use of heroin. Heroin use was positively correlated with an increase in criminal activity as measured by arrest records and self-reports. Many of the offenses for which heroin users were arrested involved the possession and sale of illicit drugs. While treatment was associated with a reduction in the use of heroin and other drugs, and with a decline in arrests for drug-related offenses, the data also show that many offenders experienced an upward trend in their criminal behavior prior to entering treatment. In most American cities, between 15 and 35 percent of persons arrested for serious crimes were current heroin users. 3 figures and 39 references