We reviewed the records of 98 consecutive patients, 18 years of age or younger, with pathologically confirmed supratentorial astroglial neoplasms at the Children's Hospital, Boston, to evaluate the importance of seizures in their presentation and natural history. Tumors were diagnosed using the WHO criteria as pilocytic astrocytomas, astrocytomas, anaplastic astrocytomas, glioblastomas, giant cell glioblastomas, oligoastrocytomas and gangliogliomas. Our results were as follows. (1) Fifty percent of children had seizures as part of their presentation and 30% had seizures as their only presenting phenomenon. (2) The seizures varied in nature, but complex (55%) or simple (28%) partial seizures were by far the most common types, occurring in 77% of cases. (3) Preoperative electroencephalography (EEG) accurately lateralized to the tumor side in 88% of the cases and localized to the correct lobe in 56%. (4) Tumors involving cerebral cortex significantly correlated with seizures at presentation as compared to noncortical locations; 59% of patients with cortical tumors presented with seizures, and only 15% of patients with noncortical tumors experienced seizures. Lesions in the temporal and frontal lobes had the highest incidence of seizures. (5) Patients with gangliogliomas and oligoastrocytomas had the highest incidence of seizures, 88 and 86%, respectively, whereas patients with anaplastic astrocytoma had the lowest incidence, 21%. (6) Histopathologic calcification was associated with seizures at presentation approaching significance (p = 0.06). (7) Seizures at presentation were significantly associated with good prognosis (p = 0.02).