The study samples consisted of 93 known hard drug users and 73 nonusers from Dutch detention centers. Data derived from structured interviews and from records of the General Documentation Register. The two groups were similar in class and educational level; the work situation of the nonusers was somewhat better than that of the users. The average age of users was 22.8 years, as compared to 26.9 years for nonusers. Study results indicate that 52.7 percent of the users had been involved in known criminal activities before using drugs, which tends to support findings in foreign literature. The differences between crime types committed by the two groups were not great. Hard drug users were more frequently involved in drug law offenses and property crimes than were nonusers, while the latter were more likely than users to commit crimes of a violent nature. The number of offenses committed by users was significantly higher than that for nonusers. Drug users involved in criminal activities before onset of hard drug use committed more crime after the onset of hard drug use committed more crime after the onset of drug use than beforehand. Users without criminal involvement before the onset of hard drug use committed approximately the same number of offenses after the onset of drug use as offenders with previous criminal records. Hard drug users are also more likely than nonusers to continue their criminal careers. Both drug use and criminal behavior are attributed to the frustrations of low-class, disadvantaged individuals whose ability to satisfy their needs for achievement and recognition is restricted by their position in life. Eventually they completely reject middle-class values and are likely to succumb to a lifestyle dominated by the need to maintain a regular supply of drugs, usually through illegal means. Progress of certain individuals to drug dependence may be the result of exposure to heroin at a susceptible developmental stage or of personal failure within the drug user's own subculture. Tables and a 15-item bibliography are supplied.