Substance use disorders (SUDs) are associated with harmful outcomes across the biopsychosocial spectrum. Although completion of treatment for SUDs is associated with beneficial outcomes such as improved well-being and reduced mortality, premature treatment termination remains high in the United States. Short-term residential treatment is brief and for more severe SUD. This 3-paper dissertation focuses on exploring covariates of treatment completion in a short-term residential setting for adults with an SUD. Secondary data include the Treatment Episode Data Set Discharges 2017 and the Short-Term Residential Treatment Dataset, which contains data gathered from a Mid-Atlantic treatment facility’s electronic medical records. Paper 1 examines the associations of sociodemographic and substance use characteristics with completion of short-term residential treatment. This paper also has a primary focus on observing sex differences in treatment completion. Results from logistic regression models indicated that men were more likely to complete treatment than were women, nonpolysubstance users were more likely to complete treatment than were polysubstance users, and individuals with alcohol identified as their primary substance were more likely to complete treatment than were individuals with other primary substances. Paper 2 examines the associations between perceived stress, distress tolerance, and treatment completion in the short-term residential SUD treatment setting. Perceived stress and distress tolerance were negatively associated. Men had lower perceived stress and higher distress tolerance than did women. Those who completed treatment had lower perceived stress and higher distress tolerance than did those who were discharged from treatment prematurely. Lower perceived stress was found to predict treatment completion conditional to including a Perceived Stress × Distress Tolerance interaction variable. Distress tolerance did not moderate the relationship between perceived stress and treatment completion. Paper 3 examines a scale based on the theory of planned behavior to predict treatment completion in the short-term residential SUD treatment setting. In a path model, the theory of planned behavior’s constructs attitude and perceived behavioral control positively predicted greater intention to complete treatment. Intention to complete treatment and perceived behavioral control did not have a direct effect on treatment completion.