In a phase III trial, children with newly diagnosed supratentorial primitive neuroectodermal tumour of the central nervous system (CNS-PNET) or pineoblastoma were randomly assigned to receive additional carboplatin during standard chemoradiotherapy after surgery, and subsequently to receive maintenance chemotherapy with or without adjuvant isotretinoin. Of 60 patients, 31 had tumours with a nonpineal location, 18 of which were high-grade gliomas (HGGs), not intended for trial inclusion. At 5 years, event-free survival was 62.8% for patients with CNS-PNETs or pineoblastoma and 5.6% for those with HGG, and overall survival was 78.5% and 12.0%, respectively. Survival outcomes were not significantly affected by therapy, which indicates that an accurate histological diagnosis is needed to spare children with HGG from receiving unnecessary treatments.