Most problem gamblers don't access treatment, often because of stigma, embarrassment or a desire to handle their problems on their own. However, research has demonstrated the effectiveness of self-help interventions for gambling problems, and this area deserves more attention because it addresses a cost-effective means of helping problem gamblers without requiring them to come to treatment. One promising self-help intervention for problem gamblers is personalized feedback. Such interventions have shown consistently positive results with other addictive behaviours, and our pilot test of personalized feedback materials for gamblers showed positive results. This randomized controlled study will evaluate the sustained efficacy of a personalized feedback intervention for problem gamblers in the general population of Ontario. It will also allow testing of the hypothesis that change in perception of gambling norms is a mediator in this process.