DATOS' goal is to determine the outcomes of drug abuse treatment delivered in typical, stable programs. It obtained data on patients in four types of treatment programs, including methadone maintenance, short-term inpatient, long-term residential, and outpatient drug-free treatment. It collected data on more than 10,000 patients at admission to treatment in nearly 100 programs in 11 cities nationwide. The most important finding from DATOS is that patients who enter drug abuse treatment do significantly reduce their illicit drug use. In each type of treatment, the use of cocaine, heroin, and other drugs in the 12 months posttreatment was significantly lower than pretreatment baseline levels. The sociodemographic and drug-use profiles of patients differ from one modality of treatment to another, indicating systematically different use of types of treatment. In addition to providing data on outcomes for drug abuse treatment as typically delivered in community-based treatment programs, there are also many questions that analysis of the DATOS database will help address in the future, such as whether there are significant economic benefits from drug abuse treatment; whether there is a clear basis for treatment matching; how program practices have changed; and the impact of legal involvement on drug abuse treatment retention, dropouts, and outcomes. 23 references