Cavernous malformations that are associated with seizures are often treated by surgical resection consisting of lesion removal, "lesionectomy," alone. Through retrospective analysis the authors have examined some factors that may predict failure to eradicate seizures by such a procedure. A group of 51 patients were examined who had been treated for supratentorial cavernous malformations with preoperative seizures and received postoperative follow up lasting at least 1 year. There was one mortality in the group. Of the remaining 50 patients, 15 (30%) had continued postoperative seizures despite therapeutic levels of antiepileptic medications. Variables that were significantly associated with continued seizures postoperatively included increasing duration of preoperative seizure history (p = 0.03), increasing number of preoperative seizures (p < 0.003), and female sex (p < 0.04). One hundred percent of patients with only one preoperative seizure or a seizure history lasting less than 2 months were seizure free following lesionectomy: approximately 75% to 80% of all patients with two to five seizures, or a seizure history lasting 2 to 12 months, were seizure free; and only 50% to 55% of those with more than five seizures or with preoperative seizure histories lasting more than 1 year were seizure free postoperatively. This investigation indicates that patients with shorter seizure histories and fewer preoperative seizures can be effectively treated by lesionectomy alone, whereas those with longer histories and more seizures are not effectively treated by this procedure and may require more extensive resections.