Among heavy gamblers with big losses, telephone and letter contact using motivational interviewing techniques to provide personalized feedback could reduce their gambling behaviour. They lost less money compared to gamblers who did not receive a phone call or letter. The telephone contact was more impactful than the letter contact. Gamblers who were interested in a follow-up call reduced their gambling behaviour further after receiving the follow-up call. Most gamblers who made changes to their gambling after receiving the intervention chose to set limits, rather than to stop gambling completely.