Intake and treatment data were collected during 1979, 1980, and 1981 for the clients of detoxification, outpatient methadone maintenance, drug-free outpatient, and drug-free residential treatment programs. Followup interviews were conducted on random samples of the clients at time periods ranging from 90 days to 4 years after treatment. Results revealed that male clients were generally older than female clients with the same drug use pattern. Prior admissions appeared to have a systematic but complex relationship with the drug use pattern; the relationship varied by treatment method. The number of drug-related problems a client had in the year before treatment was positively related to the severity of drug use. Weeks of full-time work did not appear to have any relationship to the severity or type of drug use. Finally, high involvement in a drug use network was strongly related to the severity index for the year before treatment. Tables, appended methodological information and additional results, and 32 references