Most pilocytic astrocytomas (piloA) are benign growths (World Health Organization [WHO] grade 1) of the deep midline structures, the brainstem, and the cerebellum. To the authors' knowledge, the literature contains only scarce data regarding piloA in adults. Between 1995 and 2005, 44 patients (26 women and 18 men) underwent surgery for a primary or recurrent piloA at the authors' institution. All patients were aged > 16 years (mean +/- standard deviation: 31 +/- 14 years) at the time of their first surgery. The histopathologic diagnoses were reviewed, and relevant clinical information was obtained through a chart review and telephone interviews. The mean follow-up was 76 +/- 59 months (range, 1-227 months). There were 20 patients (45%) with supratentorial lobar piloA (including 10 temporal/temporomesial tumors, 5 parietal tumors, 3 insular tumors, 1 frontal tumor, and 1 occipital tumors), 12 patients with cerebellar piloA, 7 patients with brainstem piloA, 2 patients with opticochiasmatic PiloA, 1 patient with intramedullary piloA, and 2 patients with piloA of the basal ganglia. All but 1 patient with a lobar tumor presented with epilepsy. In 6 of 44 patients (14%), increased proliferative activity was revealed. WHO grade 3 primary anaplastic piloA was diagnosed in 2 patients (5%), and WHO grade 3 secondary anaplastic piloA was diagnosed in 4 patients (9%). Tumor recurrence or disease progression was observed in 13 of 44 patients (30%). Eight of 44 patients (18%) died from their disease. Histologic grading and extent of surgical resection proved to be important predictors of survival. PiloA in adult patients, surprisingly, often was not a benign disease. The degree of surgical resection was found to be of major importance for the patient's further clinical course; therefore, an aggressive surgical resection should be attempted whenever possible.