Criminality indicators before, during, and after treatment were compared in an effort to clarify issues regarding drug use and criminal behavior. These included differences in criminality associated with characteristics of drug users, relationships between criminal activity and other behaviors such as drug use and employment, differences in criminality by type and duration of treatment received, and the impact of treatment on the reduction of criminal activity. Information was gathered from the DARP research file of comprehensive data recorded during five years of the DARP on a research sample of 27,460 clients in pretreatment and during-treatment periods and from followup interviews of 1,394 former clients admitted to treatment during the first 2 years of DARP. Data included arrests under categories of charges and reported illegal sources of support. The study found that reported illegal income sources dropped sharply from 2 months before admission to the first 2 months in treatment. The prevalence per 2-month period of illegal support, arrests, and time in jail showed no change over the first year in DARP outpatient treatment. For most individuals who stayed in methadone maintenance treatment 6 months or longer, there was little or no indication of criminality during treatment. In addition, the prevalence of criminality indicators was inversely related to the length of stay in treatment from the outset of methadone maintenance treatment. Additional findings, 9 tables, and 16 references are included.