Motivational interviewing (MI) is a promising brief intervention for people who wish to cut down or quit gambling. The study was a randomized clinical trial that tested the efficacy of a single face-to-face MI compared with a control interview (CI) for reducing gambling behaviours in individuals who expressed concerns about their gambling. Eighty-one media recruited gamblers were followed at 1, 3, 6 and 12 months post-intervention. At 12 months post-intervention participants in the MI condition spent significantly less money on gambling per month, gambled fewer days per month, and reported significantly less distress than participants in the CI condition. Participants in both conditions showed overall reduction in gambling problem severity.