Disordered gambling has been linked to increased negative affect, and some promising treatments have been shown to be effective at reducing gambling behaviors and related problems (Larimer et al. in Addiction 107:1148–1158, 2012). The current study seeks to expand upon the findings of Larimer et al. (Addiction 107:1148–1158, 2012) by examining the relationship between gambling-related problems and mental health symptoms in college students. Specifically, the three-group design tested the effects of two brief interventions for gambling—an individual, in-person personalized feedback intervention (PFI) delivered using motivational interviewing and group-based cognitive behavioral therapy, versus assessment only on mood outcomes. The mediating effect of gambling-related problems on mood was also explored. Participants (N = 141; 65 % men; 60 % Caucasian, 28 % Asian) were at-risk college student gamblers [South Oaks Gambling Screen (Lesieur and Blume in Am J Psychiatry 144:1184–1188, 1987) C3], assessed at baseline and 6-month follow-up. Gambling problems were assessed using the Gambling Problems Index (Neighbors et al. in J Gamb Stud 18:339–360, 2002). Mental health symptoms were assessed using the depression, anxiety, and hostility subscales of the Brief Symptom Inventory (Derogatis in Brief Symptom Inventory (BSI): administration, scoring, and procedures manual, National Computer Systems, Inc., Minneapolis, 1993). Results revealed that the PFI condition differentially reduced negative mood, and that reductions in gambling-related problems partially mediated this effect. Implications for intervention for comorbid mood and gambling disorders are discussed.