A prison survey by the Bureau of Justice Statistics offered the conservative estimate that 150,000 inmates needed drug treatment but did not receive it in 1997. A more liberal estimate, based on the questionable assumption that 75 percent of the State prison population requires drug treatment in any given year, is that 680,000 inmates needed but did not receive drug treatment in 1997. Regarding screening and assessment of offenders, this review suggests that an ideal approach includes an assessment of risk predictors, criminogenic needs, and a psychological evaluation. Screening and assessment instruments are most effective when they have been standardized and tested for their ability to identify offender needs and match them to appropriate treatment. Research shows that highly intensive residential programs are the most effective in reducing drug abuse and criminal behavior in the long term; however, most prisons do not offer this type of treatment, or offer it to only a small percentage of inmates. A combination of pharmacological treatment and psychosocial/behavioral therapy typically are effective for most types of drug abuse. Research shows that treatment need not be voluntary in order to be effective. Many researchers note that postrelease supervision of drug-abusing offenders is inadequate and that few offenders receive postrelease drug treatment or reentry services. For any sustained strategy of drug treatment in a correctional setting, a comprehensive and systematic approach holds the most promise. Barriers to such an approach exist in the following arenas: political, resources, assessment, administrative and organizational, and programmatic. 115 references and key research questions for each issue addressed