Gangliogliomas are indolent neoplasms that are often associated with long-standing intractable seizures. The seizure-free outcome following ganglioglioma resection alone (or "lesionectomy") has been generally favorable, ranging in most series from 50% to 65%. Thus, the value of resection of epileptogenic cortex in addition to tumor with regard to seizure outcome has been the subject of controversy. The authors describe a series of 12 patients with frontal or temporal lobe gangliogliomas associated with long-standing intractable seizures. In these patients, intraoperative electrocorticography was used to guide the resection of epileptogenic cortex along with tumor. Functional brain mapping, interictal and ictal monitoring of seizures, as well as thorough neuropsychological assessments were performed prior to resection in all cases. Outcome with regard to seizures, tumor recurrence, and neurological deficits was assessed with a mean follow-up period of 3.1 years. There was universal freedom from seizures postoperatively in 11 patients in whom complete or near-complete resection of epileptogenic cortex was achieved. In one patient in whom complete tumor resection and subtotal removal of epileptogenic cortex was achieved, a 95% reduction in seizure frequency was identified. No tumor recurrence or neurological deficits were observed. In a subset of four patients, neuropsychological and cognitive function were evaluated pre- and postoperatively. In these four, a clear trend toward improvement was noted in most functions. Thus, resection of epileptogenic cortex along with tumor may improve seizure outcome in selected patients with tumor-associated epilepsy without engendering identifiable neurological or cognitive deficits attributable to the incremental resection.