This study explored the effects on problem gambling and psychological distress when motivational interviewing (MI) was delivered at a community-based gambling help service. The researchers also explored if practitioner behaviours affected client outcomes. Participants were 146 new clients. They completed five assessments over an 18-month period. Their first calls to the service when they received the MI session were recorded and coded for practitioner behaviours. The results showed that participants improved their problem gambling severity and psychological distress. The improvements were small at 1 to 2 weeks after the MI session and were larger by the 18-month follow-up. Practitioner behaviours that did not adhere to MI principles had a negative effect on client outcomes.