Objectives: To assess the effects of a tailored, multifaceted intervention in primary care on the level of patients' alcohol consumption and to investigate which patient and organizational factors determine a reduction in alcohol consumption.Methods: This was a cluster randomized, controlled trial conducted among primary care practices in The Netherlands. Data from 6318 patients were available, of whom 712 patients from 70 practices were hazardous or harmful alcohol users. The improvement (intervention) program combined professional, organizational, and patient-directed activities. The emphasis was on educational training for general practitioners and support visits by a trained facilitator, tailored to the participants' needs and attitudes. The primary outcome was the proportion of patients with hazardous or harmful alcohol consumption, as measured with the Alcohol Use Disorders Identification Test, who reduced their levels of alcohol consumption to low-risk levels after 2 years.Results : Excessive alcohol use is a major public health problem. In approximately 55 million adult Europeans (15% of the adult population), alcohol consumption is at least hazardous.1 It is a major risk factorThis article was externally peer reviewed.