Abstract: Background: Substance use disorders (SUDs) negatively impact veterans and their relationships with others. Although there are several evidence-based treatments for SUD symptoms, there is less research on whether reduction in SUD symptoms coincides with reduction in interpersonal difficulties. Methods: In this study we examined the relationship between SUD and relationships in a national sample of 458 veterans who received approximately 12 sessions of Cognitive Behavioral Therapy for Substance Use Disorders (CBT-SUD) through the Veterans Health Administration (VHA). Results: Parallel latent growth curve modeling (LGCM) indicated that self-reported alcohol use, drug use, and interpersonal difficulties decreased over the course of treatment. Alcohol and drug use were positively associated with each other and with interpersonal difficulties at each time point, and baseline alcohol and drug use were negatively associated with the reduction of use over time. However, there was little evidence that reductions in substance use led to a reduction in interpersonal difficulties (or vice-versa). Conclusions: Findings highlight promising strategies to further understand how CBT-SUD may enhance reductions in substance use as well as improve relationships with family and friends.