Typical clinical characteristics, neuroradiologic findings, and initial neuroradiologic studies were reviewed for 40 patients <3 years of age with intracranial ependymomas, who were treated in the Pediatric Oncology Group (prolonged postoperative chemotherapy and delayed radiation for children <3 years of age with malignant brain tumors), The study included 16 females and 24 males, aged 3 to 35 months, who were diagnosed and registered in the study between 1986 and 1990. Commonly, patients presented with vomiting (70%), ataxia (53%), headache (28%), lethargy (28%), increased head circumference (23%), and irritability (23%). Duration of symptoms before diagnosis ranged from 1 day to 11 months, Thirty-five tumors (88%) were infratentorial; average tumor size was 4.3 (+/- 1.4) x 4.2 (+/- 1.7) x 4.1 (+/- 1.8) cm at presentation, Noncontrast CT scans were performed on 23 patients; 13 (57%) were isodense to surrounding brain tissue and 13 (57%) were calcified, Contrast CT scans of 29 patients revealed that 28 (97 %) were enhanced, Of the 15 T-1-weighted MRI scans, 10 (67%) demonstrated low-signal intensity tumors, and 15 (94%) of the 16 T-1-weighted scans revealed high-signal tumors, Forty-three percent of the tumors were cystic, Blood was observed within only 2 tumors and peritumoral edema was uncommon, Twenty-five percent of the ependymomas extended out to involve the dura, and 97% of the infratentorial tumors showed characteristic plasticity, Hydrocephalus was present in 34 (85%) children. (C) 1998 by Elsevier Science Inc. All rights reserved.