To evaluate survival distributions, long-term socioeconomic consequences, and health care costs in patients with childhood and adolescent onset of brain tumours in a Danish nationwide prospective cohort study. A search of national registries identified 2283 patients (1198 males, 1085 females; mean age 9 years 6 months [SD 5 years 7 months]) diagnosed with a brain tumour between 1980 and 2015 and aged no older than 18 years at diagnosis. These were compared with sex-, age-, and residency-matched comparison individuals. Patients with malignant tumours were compared with those with benign tumours. Survival distributions were estimated by the Kaplan-Meier method and hazard ratio by the Cox proportional hazard model. Socioeconomic data at age 20 and 30 years were assessed. The probability of mortality was highest during the first year after tumour diagnosis. In young adulthood, the patients were generally less likely to be married, had lower grade-point averages, educational levels, and income, were less likely to be in employment, and had higher health care costs than comparison individuals. Patients with malignant tumours had worse outcomes with respect to education, employment, and health care costs than those with benign tumours. A diagnosis of brain tumour in childhood and adolescence adversely affects survival and has negative long-term socioeconomic consequences, especially in patients with malignant tumours. These patients require continuous social support.