AIMS: To determine the effectiveness of Motivational Enhancement Therapy (MET) for hazardous drinkers in Primary Care Unit (PCU) settings in rural Thailand. METHODS: A randomized controlled trial was conducted in eight PCUs in Ubonratchatanee and Chachoengsao provinces in Thailand. Hazardous drinkers were identified using the World Health Organization-recommended Alcohol Use Disorder Identification Test. Of 117 eligible participants (91% male), 59 were randomized to the intervention group to receive MET in three individual appointments with a trained nurse and 58 to an assessment-only control group. Outcome evaluations were carried out after 6 weeks, 3 months and 6 months. RESULTS: Follow-up data were available on 84, 94 and 91% of subjects, respectively, at the three intervals. Self-reported drinks per drinking day, frequency of hazardous drinking assessed either on a daily or weekly basis, and of binge drinking sessions were reduced in the intervention group more than in the control group (P < 0.05) after both 3 and 6 months. The groups did not generally differ at 6 weeks. However, although self-reported consumption in both groups fell from baseline to 6-month follow-up, serum gamma-glutamyl transferase increased in both groups, which raises doubts about the validity of this marker in this sample and/or the validity of the self-reported data in this study. CONCLUSION: MET delivered by nurses in PCUs in Thailand appears to be an effective intervention for male hazardous drinkers. Uncertainties about the validity of self-reported data jeopardize the safety of this conclusion.