The histopathological, clinical, and radiological findings in 25 patients (median age 20.5 years; range 1.7-64.2 years) with gangliogliomas were assessed to correlate degree of astrocytic anaplasia and proliferative potential with recurrence or survival. Most patients (64%) presented with seizures (median Karnofsky Performance Score 90%; range 70-100%). Computerized tomography and magnetic resonance imaging showed nonspecific abnormalities. Neoplastic ganglion cells were defined as heterotopic, irregularly grouped, or having more than one nucleus of bizarre shape or size. The astrocytic component was moderately anaplastic in 15 cases and highly anaplastic (HAA) in 10. Eight patients had gross total resection, 11 had subtotal resection, and six underwent biopsy. Ten patients (five gross total resection, three subtotal resection, two biopsy) had no further treatment, 15 underwent external irradiation, and five had adjuvant chemotherapy. Twenty-four patients are alive 15-394 weeks (median 203.5 weeks) postoperatively; one with ganglioglioma-HAA died at 65 weeks. No tumor recurred after gross total resection. Duration of preoperative symptoms < 1 year, greater anaplasia, and age > 30 years at diagnosis may have increased the risk of recurrence after subtotal resection or biopsy by four, three, and two times, respectively (not significant). Bromodeoxyuridine labeling index (BUdR LI) was < 1% in eight non-recurring tumors and 1.3% in another recurring twice (second recurrence LI = 1.6%). Most patients with ganglioglioma have a good prognosis. After gross total resection, only observation is required. After subtotal resection or biopsy, recurrence is possible. BUdR labeling may guide further therapy.