Background: Routine outcome monitoring (ROM) is an important component of service provision and qualitity assurance procedures. However, a major logistical and financial challenge for organizations is successfully following up participants once they have left residential alcohol and other drug treatment. The aim of the current study was to assess the impact and effectiveness of an “early” follow-up contact and brief interview on subsequent 3-month ROM follow-up success. Methods: Participants were 800 clients attending specialist residential alcohol and other drug treatment provided by The Salvation Army. As part of routine outcome assessment procedures, all people attending these programs are asked to complete a 3-month follow-up assessment. Participants were randomly allocated either to the early contact condition (i.e., “early” 2-week follow-up contact prior to the 3-month follow-up assessment) or to the control condition (i.e., no “early” 2-week follow-up prior to the 3-month follow-up assessment). The primary outcomes were the proportion of participants who were followed up and surveyed at 3 months. Results: There were significantly higher follow-up rates at 3 months post discharge for participants in the early contact group (55.6%) compared with the control condition (46.1%). Although there were higher rates of 3-month follow-up for participants in the early contact group, rates of successful survey completion were not significantly different between the 2 groups. Conclusions: Including an early 2-week telephone call prior to the 3-month assessment increased the number of participants we were able to follow up at 3 months post discharge but did not improve the rate of survey participation at 3 months. The additional costs associated with this activity and the modest increase in follow-up rates need to be considered prior to organizations investing in these follow-up enhancement activities.