A total of 16,729 persons were admitted to drug abuse treatment programs registered with the Drug Abuse Reporting Program (DARP) during the period June 1972 through March 1973. From this population base, a stratified random sample was selected for follow-up, composed of 2,295 former patients from 26 DARP agencies. The follow-up sample included black and white persons of both sexes from methadone maintenance programs, therapeutic communities, outpatient drug-free treatments, and outpatient detoxification programs. Assignment of patients to treatment groups was performed in accordance with each clinic's regular procedures and was not random. Sixty-one percent of the sample had achieved abstinence from opioid drugs for a year or longer immediately before the follow-up interview. Compared with those who continued heavy opioid drug use, as well as with others who had problems with nonopioid drugs or alcohol over time, persons who achieved abstinence also had significantly better long-term outcomes on criminality, use of nonopioid drugs and alcohol, and productive activities. Except for criminal history, outcome status was generally unrelated to client demographic and background predictors, but behavioral improvement over time was strongly associated with participation in drug abuse treatment. The findings add further correlational evidence in the overall DARP research program to the contribution of treatment to the improvement of prosocial behaviors of drug abusers. 28 references