BACKGROUND: Over the last 30  years the number of people who drink alcohol at harmful levels has increased in many countries. There have also been large increases in rates of sexually transmitted infections. Available evidence suggests that excessive alcohol consumption and poor sexual health may be linked. The prevalence of harmful alcohol use is higher among people attending sexual health clinics than in the general population, and a third of those attending clinics state that alcohol use affects whether they have unprotected sex. Previous research has demonstrated that brief intervention for alcohol misuse in other medical settings can lead to behavioral change, but the clinical- and cost-effectiveness of this intervention on sexual behavior have not been examined. METHODS: We will conduct a two parallel-arm, randomized trial. A consecutive sample of people attending three sexual health clinics in London and willing to participate in the study will be screened for excessive alcohol consumption. Participants identified as drinking excessively will then be allocated to either active treatment (Brief Advice and referral for Brief Intervention) or control treatment (a leaflet on healthy living). Randomization will be via an independent and remote telephone randomization service and will be stratified by study clinic. Brief Advice will comprise feedback on the possible health consequences of excessive alcohol consumption, written information about alcohol and the offer of an appointment for further assessment and Brief Intervention. Follow-up data on alcohol use, sexual behavior, health related quality of life and service use will be collected by a researcher masked to allocation status six months later. The primary outcome for the study is mean weekly alcohol consumption during the previous three months, and the main secondary outcome is the proportion of participants who report unprotected sex during this period. DISCUSSION: Opportunistic intervention for excessive alcohol use has been shown to be effective in a range of medical settings. The SHEAR study will examine whether delivering such interventions in sexual health clinics results in reductions in alcohol consumption and will explore whether this is associated with changes in sexual behavior.