BackgroundAsthma is the most common chronic disease in children, many of whom are managed solely with a short-acting β₂-agonist (SABA). In adults, the evidence that budesonide-formoterol as sole reliever therapy markedly reduces the risk of severe exacerbations compared with SABA alone has contributed to the Global Initiative for Asthma recommending against SABA monotherapy in this population. The current lack of evidence in children means it is unknown whether these findings are also relevant to this demographic. High-quality randomised controlled trials (RCTs) are needed.ObjectiveThe aim of this study is to determine the efficacy and safety of as-needed budesonide-formoterol therapy compared with as-needed salbutamol in children aged 5 to 15 years with mild asthma, who only use a SABA.MethodsA 52-week, open-label, parallel group, phase III RCT will recruit 380 children aged 5 to 15 years with mild asthma. Participants will be randomised 1:1 to either budesonide-formoterol (Symbicort Rapihaler^®) 50/3 µg, two actuations as needed, or salbutamol (Ventolin^®) 100 µg, two actuations as needed. The primary outcome is asthma attacks as rate per participant per year. Secondary outcomes assess asthma control, lung function, exhaled nitric oxide and treatment step change. A cost-effectiveness analysis is also planned.ConclusionThis is the first RCT to assess the safety and efficacy of as-needed budesonide-formoterol in children with mild asthma. The results will provide a much-needed evidence base for the treatment of mild asthma in children.