OBJECTIVE: To evaluate the influence of preoperative abstinence on postoperative outcome in alcohol misusers with no symptoms who were drinking the equivalent of at least 60 g ethanol/day. DESIGN: Randomised controlled trial. Setting: Copenhagen, Denmark. SUBJECTS: 42 alcoholic patients without liver disease admitted for elective colorectal surgery. INTERVENTIONS: Withdrawal from alcohol consumption for 1 month before operation (disulfiram controlled) compared with continuous drinking. MAIN OUTCOME MEASURES: Postoperative complications requiring treatment within the first month after surgery. Perioperative immunosuppression measured by delayed type hypersensitivity; myocardial ischaemia and arrhythmias measured by Holter tape recording; episodes of hypoxaemia measured by pulse oximetry. Response to stress during the operation were assessed by heart rate, blood pressure, serum concentration of cortisol, and plasma concentrations of glucose, interleukin 6, and catecholamines. RESULTS: The intervention group developed significantly fewer postoperative complications than the continuous drinkers (31% v 74%, P=0.02). Delayed type hypersensitivity responses were better in the intervention group before (37 mm2 v 12 mm2, P=0.04), but not after surgery (3 mm2 v 3 mm2). Development of postoperative myocardial ischaemia (23% v 85%) and arrhythmias (33% v 86%) on the second postoperative day as well as nightly hypoxaemic episodes (4 v 18 on the second postoperative night) occurred significantly less often in the intervention group. Surgical stress responses were lower in the intervention group (P</=0.05). CONCLUSIONS: One month of preoperative abstinence reduces postoperative morbidity in alcohol abusers. The mechanism is probably reduced preclinical organ dysfunction and reduction of the exaggerated response to surgical stress.