A retrospective clinical analysis was made of 12 patients with supratentorial primitive neuroectodermal tumor (PNET) who ranged in age from 20 to 62 years (median 24) and were managed at Seoul National University Hospital between January 1987 and December 1997. Six patients were male and six were female. Most presented with symptoms of increased intracranial pressure and mean duration of symptoms was four months (range: 1-12 months). The tumors were located in the posterior parieto-occipital area in six cases and the mean diameter of mass of these tumors was 5.3 cm. The characteristic magnetic resonance image finding was a large well-demarcated lobulating mass with intratumoral cyst, necrosis, and/or hemorrhage. Calcification was seen in five out of six patients who underwent computed tomography scan. All patients underwent craniotomy and three of them received subsequent operations due to local recurrence. Ten patients received postoperative whole neuraxis radiation therapy and five patients received additional chemotherapy. Mean survival after diagnosis was 86 months. The patients having intratumoral calcifications are all alive and two out of three showing a Ki-67 labelling index greater than 30% died at eight and 20 months after operation, respectively. In conclusion, supratentorial PNET must be included, even in adults, in the differential diagnoses if a tumor has characteristic radiological features. The adult supratentorial PNET seemed similar to that of children in the clinical features and the prognosis. Intratumoral calcifications and the Ki-67 labelling index might be prognostic factors, however, it should be considered that the sample size is too small and not all patients were evaluated.