Approximately 50% of individuals with first-episode psychosis meet criteria for a substance use disorder and these concurrent disorders are associated with worse long-term outcomes. Psychosocial interventions, including motivational interviewing as well as cognitive and behavioural therapies, have shown some evidence for effective treatment in substance use disorders; however, there is a paucity of existing studies that have successfully examined these interventions in first-episode psychosis. Participants (n=64) received the concurrent disorders intervention, which included individual support alongside participation in at least one of two groups: a 4-week Motivational Engagement group utilizing motivational interviewing (n=59) and an 8-week Relapse Prevention Training group emphasizing skill acquisition, which some participants entered directly (n=5) and some participants entered following completion of the Motivational Engagement group (n=16). Participants who completed the Motivational Engagement group (n=59) demonstrated significantly increased motivation to change substance use (d=-.0.58; t=-3.02, p < .01) and significantly decreased substance use frequency (d=0.65; t=3.26, p < .01). For participants who completed the Relapse Prevention Training group (n=21), substance use frequency significantly decreased (d=0.92; t=3.46, p < .01) and self-efficacy in one's ability to maintain substance use changes significantly increased (d=-0.85; t=-3.59, p < .01). This pilot evaluation suggests that motivational interviewing and relapse prevention skills training are acceptable and feasible interventions in the treatment of substance use disorders in young adults with first-episode psychosis.