When psychosis emerges in young people there is a risk of poorer outcomes, and access to evidence-based treatments is paramount. The current evidence base is limited. Antipsychotic medications show only a small benefit over placebo, but young people experience more side effects than adults. There is sparse evidence for psychological intervention. Research is needed to determine the clinical effectiveness and cost-effectiveness of psychological intervention versus antipsychotic medication versus a combined treatment for adolescents with psychosis. The objective of Managing Adolescent first-episode Psychosis: a feasibility Study (MAPS) was to determine the feasibility of conducting a definitive trial to answer the question of clinical effectiveness and cost-effectiveness of these three treatment options. This was a prospective, randomised, open-blinded, evaluation feasibility trial with a single blind. Participants were allocated 1 : 1 : 1 to receive antipsychotic medication, psychological intervention or a combination of both. A thematic qualitative study explored the acceptability and feasibility of the trial. Early intervention in psychosis services and child and adolescent mental health services in Manchester, Oxford, Lancashire, Sussex, Birmingham, Norfolk and Suffolk, and Northumberland, Tyne and Wear. People aged 14-18 years experiencing a first episode of psychosis either with an International Classification of Diseases, Tenth Revision, schizophrenia spectrum diagnosis or meeting the entry criteria for early intervention in psychosis who had not received antipsychotic medication or psychological intervention within the last 3 months. Psychological intervention involved up to 26 hours of cognitive-behavioural therapy and six family intervention sessions over 6 months, with up to four booster sessions. Antipsychotic medication was prescribed by the participant's psychiatrist in line with usual practice. Combined treatment was a combination of psychological intervention and antipsychotic medication. The primary outcome was feasibility (recruitment, treatment adherence and retention). We used a three-stage progression criterion to determine feasibility. Secondary outcomes were psychosis symptoms, recovery, anxiety and depression, social and educational/occupational functioning, drug and alcohol use, health economics, adverse/metabolic side effects and adverse/serious adverse events. We recruited 61 out of 90 (67.8%; amber zone) potential participants (psychological intervention, n = 18; antipsychotic medication, n = 22; combined treatment, n = 21). Retention to follow-up was 51 out of 61 participants (83.6%; green zone). In the psychological intervention arm and the combined treatment arm, 32 out of 39 (82.1%) participants received six or more sessions of cognitive-behavioural therapy (green zone). In the combined treatment arm and the antipsychotic medication arm, 28 out of 43 (65.1%) participants received antipsychotic medication for 6 consecutive weeks (amber zone). There were no serious adverse events related to the trial and one related adverse event. Overall, the number of completed secondary outcome measures, including health economics, was small. Medication adherence was determined by clinician report, which can be biased. The response to secondary outcomes was low, including health economics. The small sample size obtained means that the study lacked statistical power and there will be considerable uncertainty regarding estimates of treatment effects. It is feasible to conduct a trial comparing psychological intervention with antipsychotic medication and a combination treatment in young people with psychosis with some adaptations to the design, including adaptations to collection of health economic data to determine cost-effectiveness. An adequately powered definitive trial is required to provide robust evidence. Current Controlled Trials ISRCTN80567433. This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 25, No. 4. See the NIHR Journals Library website for further project information.