This study examined factors associated with methadone maintenance retention, defined as remaining in treatment for a minimum of 90 days, among street recruited injection drug users (IDUs). Targeted sampling methods were used to establish recruitment quotas in Denver census tracks. A total of 577 IDUs were randomly assigned to either a risk reduction intervention, focusing on safer injection and sex behaviors, or motivational interviewing, addressing more sweeping lifestyle changes including drug treatment. All subjects who wanted treatment were provided transportation, rapid intake and a waiver of the intake fee. In addition, 50% were randomly assigned a coupon for 90 days of free treatment. Overall, 33% entered treatment and of these, 60% remained for at least 90 days. Factors associated with retention included higher methadone dose, free treatment, greater contacts with the clinic and counselor rating of patient cooperation. Although desire for treatment, or motivation, was associated in univariate analyses with greater retention, there were no differences observed between the motivational interviewing and risk reduction interventions.