OBJECTIVE Tumors of central nervous system (CNS) are accounted as the second most common tumors in childhood (21% of all cancers) following hematologic malignancies. The patients can suffer more than one cancer in their lifetime, and radiotherapy is claimed for de novo formation of a new tumor in years after treatment of an initial tumor. METHODS We have retrospectively analyzed our database for defining radiotherapy-related de novo brain tumors operated in between January, 2000 and August, 2012. New tumors in the field of radiotherapy were included into the study. RESULTS The retrospective analysis revealed six patients (two girls and four boys) eligible for further evaluation. The children were irradiated at an age in the range of 5 and 12 years (mean, 7.8). The primary diagnoses were hematological malignancies in two (acute lymphocytic leukemia and non-Hodgkin lymphoma (NHL)) and solid tumors in other four (two pilocytic astrocytoma, one craniopharyngioma, and one grade 3 astrocytoma). All patients received cranial radiotherapy. The mean latency period for the "second tumor" was 9.5 years. The pathological diagnoses for de novo new tumors were as follows: glial tumor (two cases), medulloblastoma (two cases), mesenchymal tumor (one case), and meningeal sarcoma (one case). All de novo tumors were high graded. Mean survival was 14.6 months. CONCLUSIONS de novo brain tumors after irradiation has poor prognosis in neurosurgical practice. Vigilance and awareness for possibility of de novo new tumor are warranted for both families and physicians at follow-ups even years after the treatment of initial tumors.