BackgroundA 2014 enquiry by the Children, Young People and Education Committee of the National Assembly for Wales raised issues relating to increased psychotropic prescribing in children and young people. We aimed to use routinely collected health-care data to explore trends in the incidence and prevalence of psychotropic prescriptions (antidepressants, anxiolytics, medication for attention deficit hyperactivity disorder, antipsychotics) in this age-group in primary care in Wales to inform policy and practice. MethodsFour retrospective e-cohort studies were conducted with the Secure Anonymised Information Linkage (SAIL) databank. Individuals aged up to 18 years, registered with a general practitioner supplying data to SAIL (195 general practice populations out of 495 practices) between Jan 1, 2003, and Dec 31, 2013, were identified. Annual incidence rates were calculated as person-years at risk. Poisson regression was undertaken to investigate the adjusted associations between incidence of prescription and year of record, sex, age, and deprivation. FindingsRates of antipsychotic prescriptions increased modestly over the study period (incidence rate ratio 1·21, 95% CI 0·95–1·52) with significant increases only seen in 15–17 year-olds (1·39, 1·07–1·80). Prescriptions for typical antipsychotics decreased alongside a nearly double increase for atypical antipsychotics. Incident prescriptions were significantly higher in boys than in girls (1·40, 1·28–1·53) and in deprived than in non-deprived areas (1·59, 1·38–1·82). Rates of diagnosis of attention deficit hyperactivity disorder remained stable (1·06, 0·91–1·24). Incident rates of prescribing with stimulants and atomoxetine increased (1·25, 1·06–1·47). Incidence of prescribing more than doubled in 15–18 year-olds (2·53, 1·58–4·05). Similarly significant increases in prescribing over time were seen in 15–18 year-olds for antidepressants and anxiolytics. InterpretationSupport for older adolescents should be made available at a primary care level, particularly in more deprived communities. Such support could assist in the transition to adult services when required. We found some evidence of prescribing outside current guidelines. These e-cohort studies resulted in the publication of Welsh Health Circulars relating to prescribing, evidence was given at the National Assembly, and a Welsh Medicines Resource Centre (WeMeRec) bulletin (plus case study) was issued to implement change. Routine data does not explicitly link medication prescription with diagnosis. FundingWelsh Government. The funder did not have any influence on study design; collection, analysis, or interpretation of data; or the preparation, review, or approval of the abstract.