We present the cost and cost-effectiveness of referral to an alcohol health worker (AHW) and information only control in alcohol misusing patients. The study was a pragmatic randomised controlled trial conducted from April 2001 to March 2003 in an accident and emergency department (AED) in a general hospital in London, England. A total of 599 adults identified as drinking hazardously according to the Paddington Alcohol Test were randomised to referral to an alcohol health worker who delivered a brief intervention (n = 287) or to an information only control (n = 312). Total societal costs, including health and social services costs, criminal justice costs and productivity losses, and clinical measures of alcohol consumption were measured. Levels of drinking were observably lower in those referred to an AHW at 12 months follow-up and statistically significantly lower at 6 months follow-up. Total costs were not significantly different at either follow-up. Referral to AHWs in an AED produces favourable clinical outcomes and does not generate a significant increase in cost. A decision-making approach revealed that there is at least a 65% probability that referral to an AHW is more cost-effective than the information only control in reducing alcohol consumption among AED attendees with a hazardous level of drinking.