Background: Alcohol is a major global threat to public health. Although the main burden of chronic alcohol-related disease is in adults, its foundations often lie in adolescence. Alcohol consumption and related harm increase steeply from the age of 12 until 20 years. Several trials focusing upon young people have reported significant positive effects of brief interventions on a range of alcohol consumption outcomes. A recent review of reviews also suggests that electronic brief interventions (eBIs) using internet and smartphone technologies may markedly reduce alcohol consumption compared with minimal or no intervention controls. Interventions that target non-drinking youth are known to delay the onset of drinking behaviours. Web based alcohol interventions for adolescents also demonstrate significantly greater reductions in consumption and harm among 'high-risk' drinkers; however changes in risk status at follow-up for non-drinkers or low-risk drinkers have not been assessed in controlled trials of brief alcohol interventions. Design and methods: The study design comprises two linked randomised controlled trials to evaluate the effectiveness and cost-effectiveness of two intervention strategies compared with screening alone. One trial will focus on high-risk adolescent drinkers attending Emergency Departments (Eds) and the other will focus on those identified as low-risk drinkers or abstinent from alcohol but attending the same ED. Our primary (null) hypothesis is similar for both trials: Personalised Feedback and Brief Advice (PFBA) and Personalised Feedback plus electronic Brief Intervention (eBI) are no more effective than screening alone in alcohol consumed at 12 months after randomisation as measured by the Time-Line Follow-Back 28-day version. Our secondary (null) hypothesis relating to economics states that PFBA and eBI are no more cost-effective than screening alone. In total 1,500 participants will be recruited into the trials, 750 high-risk drinkers and 750 low-risk drinkers or abstainers. Participants will be randomised with equal probability, stratified by centre, to either a screening only control group or one of the two interventions: single session of PFBA or eBI. All participants will be eligible to receive treatment as usual in addition to any trial intervention. Individual participants will be followed up at 6 and 12 months after randomisation. Discussion: The protocol represents an ambitious innovative programme of work addressing alcohol use in the adolescent population. Trial registration: ISRCTN45300218. Registered 5th July 2014.