In children, treatment regimen for high-grade gliomas (HGG) and diffuse intrinsic pontine gliomas (DIPG) are generally not stratified according to disease stage. The hypothesis was that secondary disseminating disease (SDD) in children with HGG is related to an even worse outcome. Description of SDD pattern was performed. In total, 270 children with newly diagnosed HGG or DIPG were eligible for retrospective analysis of SDD. Medical and computer records of these patients were reviewed for demographic characteristics, sites of dissemination, prognostic variables. Forty-six (17%) of the 270 patients had developed SDD. The median time to SDD was 8.2 months. The median overall survival (OS) after dissemination was 3.2 months. The SDD was located parenchymal in the supratentorial (34.8%), infratentorial (6.5%), supratentorial and infratentorial (19.6%), spinal (10.9%), spinal and cerebral (6.5%) regions of the CNS, or leptomeningeal (21.7%). For HGG patients, the median OS was shorter among patients with SDD than among patients without SDD (1.02 vs 1.41 years, P=0.0495). In the group of patients with SDD, patients with cerebrospinal fluid dissemination had a worse outcome compared with patients with parenchymal metastases. Summarising, SDD is a negative prognostic factor for patients with HGG outside the pons. Treatment stratification should be considered.