BACKGROUNDThe literature on skull base chondrosarcoma (CHS) is scarce. We report outcomes for pediatric and young patients ≤ 22 years with base of skull (BOS) CHSs treated with proton-based radiotherapy (PBRT). METHODSWe retrospectively reviewed all patients treated with PBRT between 1981 and 2023. Primary endpoints were overall survival (OS), chondrosarcoma-specific survival (CSS), progression-free survival (PFS), local control (LC), and distal control (DC). RESULTSEighty-four patients were identified. Median age at diagnosis was 19 years (range, 6 - 22). Most patients (n=79, 94%) had conventional CHS while 5 (6%) had mesenchymal CHS. Nine patients (11%) underwent gross total resection (GTR), 64 (76%) subtotal resection (STR) and 11 patients (13%) underwent biopsy. Twenty-four (29%) patients progressed prior to radiotherapy (RT). The median prescription dose was 70 Gy (RBE) (range, 50 – 79.7). At a median follow-up of 18.0 years [interquartile range (IQR),), 9.2 –26.2] from diagnosis, 11 patients recurred (7 local, 4 distant). Six patients died of disease. Five patients died of other causes. Ten-year OS, CSS and PFS rates for all patients were 93.3%, 94.7% and 88%, respectively. Twenty-year OS, CSS and PFS rates for conventional CHS (n=79) were 93.1%, 97.1% and 89.2%, respectively. Mesenchymal histology was significantly associated with worse OS and PFS. Pre-RT tumor progression portended worse OS and CSS. Eight patients (9.9 %) experienced a late toxicity grade 3 or greater. CONCLUSIONSThis is the largest cohort of pediatric BOS CHSs in literature to date. High-dose PBRT following surgical resection achieves excellent disease control with minimal toxicity.