A sample of 1,496 persons admitted to 26 community treatment agencies participating in the Drug Abuse Reporting Program (DARP) during 1972 and 1973 were located and interviewed in 1978 and 1979. Favorableness of one-year posttreatment outcomes with respect to illicit drug use, criminality, and employment and other productive activities was found to increase linearly with the length of time patients stayed in methadone maintenance, a therapeutic community, or outpatient drug-free treatment. In addition, follow-up outcome for persons who spent less than three months in treatment was least favorable, and was not significantly different from that of persons in outpatient detoxification programs or who were admitted but not treated (intake-only). Persons who completed treatment generally stayed in treatment longer, as expected; they also had a more favorable outcome after DARP treatment than did others.