The population studied consists of the 230 heroin addicts who entered methadone treatment in December 1971. A total of 160 patients were selected for intensive study, including all 68 who remained in treatment, all 23 who had completed detoxification, and a random sample of 69 of the 139 who had left treatment. This last group was selected to match the number of those who remained in treatment. Demographic information and personal histories were taken from admission records. Criminal histories were obtained from the records of the Atlanta Police Department and the Georgia Crime Information Center. Comparison of the preaddiction and postaddiction criminal rates showed no changes for thefts or violent crimes. In comparing the year prior to treatment versus the time while in treatment, no changes in rates of arrests or convictions were found. Findings concerning the kinds of criminal charges against the addict population before treatment are similar to those of previous studies. The majority of nondrug crimes in the population were misdemeanors and property crimes. Violent crimes represented only 2 percent of the charges. Interviews with addicts, an examination of addict police records, and a comparison of kinds of arrests in addict versus non-addict groups confirm the predominance of robbery and property crimes among nondrug charges. There was little evidence of reduction in criminal activity of addicts while they were in treatment. These findings contrast sharply with the results of most previous studies. 6 tables and 28 references