Many studies have found that the longer a drug user remains in treatment, the more positive the outcome. The majority of studies on the effects of time in treatment have followed subjects from the time they enter treatment. The subjects of the present study are injection drug users and crack users who were out of treatment at the time of their recruitment to the study. Between the initial and six-month follow-up interviews, some chose to enroll in drug treatment. The more time a subject spent in treatment during the follow-up period, the more likely it was that s/he was not using heroin or cocaine at follow-up (OR=.51; 95% C.I., .39-.67; p<.001). Unlike the results of some prior studies, positive effects of time in treatment were found even when time in treatment was less than 90 days. The findings of the present study strongly suggest that treatment is beneficial even for those who remain for less than 90 days. Those who provide treatment services to drug users should attempt to maintain contact with dropouts, and support their return to treatment.