Residential treatment is a common option for individuals with moderate to severe substance use disorders. In a cohort of individuals who accessed residential treatment, we investigated client demographic, substance use, mental health, treatment, and psychological predictors of treatment completion. Participants were a retrospective cohort of 1056 (15-69 years) individuals admitted to residential treatment facilities across Queensland, Australia, from January 2014 to December 2016. Participant characteristic information was obtained at admission, including the Depression Anxiety Stress Scale 21 (DASS-21). A multiple logistic regression model was conducted with treatment completion as the outcome. The overall rate of treatment completion was 14.3%. Mild to moderate (aOR = 0.48 [0.28-0.84], p = .010) and severe to extremely severe (aOR = 0.35 [0.17-0.74], p = .006) stress on the DASS-21 at service entry was significantly associated with a lower likelihood of treatment completion. Participants with higher levels of stress at service entry were less likely to complete treatment, representing a missed opportunity to provide targeted support during high-risk periods for individuals with substance use disorders. Further research investigating the nature and causes of stress in-between, during, and following presentations to residential treatment is needed.