Cavernous malformations (CM) are cerebral irradiation-related late complications. Little is known about their natural history and the pathogenetic role of concomitant chemotherapy. We present a retrospective, single-institution study of 108 children affected with medulloblastoma, ependymoma, or germinoma treated with radio- and chemotherapy. The frequency, clinical and radiological presentations, and outcomes were analyzed to investigate the relationship among radiation dose, associated chemotherapy, age, latency and localization of radiation-induced CM. 100 out of 108 children were treated with radiotherapy for primary brain tumor; 34 (27 with medulloblastoma and 7 with other histologies) out of 100 patients developed CM. No significant relationship was found between CM and gender (p = 0.70), age (p = 0.90), use of specific chemotherapy (standard versus high-dose, p = 0.38), methotrexate (p = 0.49), and radiation dose (p = 0.45). However, CM developed more frequently and earlier when radiotherapy was associated with methotrexate (70 % of cases). Radiation-induced CM prevailingly occurred in the cerebral hemispheres (p = 0.0001). Only 3 patients (9 %) were symptomatic with headache. Three patients underwent surgery for intra- or extra-lesional hemorrhage. CM was confirmed by histopathology for all 3 patients. The vast majority of radiation-induced CM is asymptomatic, and macro-hemorrhagic events occur rarely. Concomitant therapy with methotrexate seems to favor their development. We recommend observation for asymptomatic lesions, while surgery should be reserved to symptomatic growth or hemorrhage.