The research was prompted by the recognition that drug treatment efforts can fail because they are not tailored to the specific needs of the drug-dependent person and that drug addicts are often classified by techniques that are poorly suited for successful rehabilitation. The study used data from arrestees interviewed during the first quarter of 1996 through the third quarter of 1997. The participants had an average age of 31.6 years and ranged in age from 19 to 77 years. More than 41 percent were Hispanic, 32 percent were white, 14 percent were black, 10 percent were Asian, and 2 percent reported another ethic group. Results revealed five clusters of drug users. The Boozers had the highest rate of use of easily obtainable drugs and had excessively high rates of alcohol abuse. The Solicitors had a moderately high rate of experimental drug use, although they had the lowest rate of needing or being under the influence of drugs or alcohol at the time of their offense. The Converters had a high rate of experimental use, the highest rates of needing or being under the influence of drugs or alcohol at the time of arrest, and committed primarily property offenses. The Violent Alcoholics tended to explode after a drunken binge and were subsequently arrested for violent offenses such as assault or domestic violence. The Enablers were likely to be under the influence of drugs or alcohol when committing their offenses rather than engaging in criminal behavior due to a need for drugs. Findings add to understanding of the need for client-specific assignment to programs. Tables, notes, and 18 references (Author abstract modified)