High rates of posttraumatic stress disorder (PTSD) have been reported among people seeking treatment for substance use disorders (SUDs), although few studies have examined the relationship between PTSD and substance use in young drug users. This study compared levels of substance use, coping styles, and high-risk triggers for substance use among 66 young adults with SUD, with or without comorbid PTSD. Young people with current SUD-PTSD (n = 36) reported significantly higher levels of substance use in negative situations, as well as emotion-focused coping, compared to the current SUD-only group (n = 30). Severity of PTSD was a significant predictor of negative situational drug use, and emotion-focused coping was found to mediate this relationship. The findings underscore the need for youth substance abuse treatment programs to include coping skills training and management of affect regulation for those individuals with comorbid SUD-PTSD.