BACKGROUND: The primary approach to reducing crime in the US has been through the criminal justice system. However, drug treatment may be an effective tool in reducing crime. In order to make better use of treatment as an alternative approach, one needs to know if reducing drug use through treatment results in decreased crime. AIMS OF THE STUDY: The objective of this paper is to model and empirically investigate the extent to which a change in drug use that results from treatment reduces crime and whether a change in drug use is causally related to change in crime. We focus on crime-for-profit. METHODS: We use a multi-site dataset of 3,502 inner-city drug users entering treatment. We analyze the change in drug use and crime pre and post treatment. We take first differences to address the omitted variable problem. RESULTS: We find that treatment reduces drug use and that, in turn, reduced drug use has a significant impact on crime. For our study population, reduced drug use seems to be causally related to reduced crime. This finding is robust to specification and subsamples. We estimate that reduced drug use due to treatment is associated with 54% fewer days of crime for profit, ceteris paribus. DISCUSSION: We use a longitudinal data set and a novel approach to analyze the relationship between crime and drugs. We analyze a low-income, inner-city, drug-addicted sample. We use self-reported crime. For our purposes, the use of individual data is an improvement over the use of aggregate level data that has been used in much of the related literature. Limitations of our paper include that we do not have a random sample and that our measure is self-reported in the previous 30 days. IMPLICATIONS FOR HEALTH POLICIES: Our findings suggest that drug treatment may be an effective crime-fighting tool. Treatment reduces not only the crime of drug possession, but also crime-for-profit. Current public policy emphasizes use of the criminal justice system, incarceration in particular, as a mechanism to combat crime. Given the huge and growing expense of the criminal justice system, drug treatment might be cost-effective relative to incarceration. California s so called Proposition 36 is based on this yet to be proven premise. Although additional research is required, our findings may help inform the debate on treatment versus criminal justice. We have provided empirically-based findings that reduced drug use due to treatment can result in important reductions in crime. Our findings can serve as a building block for policy development.