The study sample included 119 males and 117 females who were prescribed opiates (including methadone) during the course of their treatment at two drug dependence clinics in London, England, between 1968 and 1975. Data on the stages of treatment and on outcome were obtained from Home Office and Criminal Records Office files. Convictions were classified either as drug offenses, which included prescription forgery and the burglary of chemists' shops, or as nondrug offenses, which included violent and property crimes, aggressive and nuisance offenses, prostitution and sex offenses, driving offenses, and breaches of probation. Subjects' criminal careers were divided into four stages: the period between the age of criminal responsibility and the first illicit use of any drug, between first illicit drug use and entry into treatment, the period of treatment, and between leaving clinic treatment and the end-point of the study. The results showed that male patients had commenced their drug use at a mean age of 17.3 years and that by this time 32 percent had been convicted. This compares to 14.9 percent of males in a national sample who had a conviction before the age of 21. Females commenced drug use at a mean age of 16.7 years, and 12 percent had a conviction before any drug use. In the national sample, 1.6 percent of the girls under the age of 17 had received convictions. By the end of the study, 94 percent of the men and 76 percent of the women had at least one conviction; 71 percent of all convictions were for nondrug offenses. During treatment, the overall crime rate was not reduced, and a significant increase in the proportion of drug offenses was noted even though opiates were being prescribed. This finding calls into question the assumption that a free supply of drugs from licit sources will minimize illicit drug-seeking behavior. Finally, for females, the absence of a criminal record for nondrug offenses at the time of their first clinic contact was found to indicate a favorable prognosis. Related studies are reviewed. Data tables and 29 references are included.