We designed our study to analyze the prognostic factors and treatment outcomes of adult medulloblastoma patients who received postoperative craniospinal irradiation. Fourty-three patients who were treated due to medulloblastoma at Istanbul University, Institute of Oncology between 1990 and 2013 were retrospectively analyzed. All of the patients were older than 18 years, with a median age of 27 years (range, 18-51 years). In 40 (93%) patients, total resection of the tumor was achieved, and 3 (7%) patients had undergone a subtotal tumoral resection. Risk assessment revealed 7 high-risk and 36 standard-risk patients. All patients received postoperative craniospinal irradiation, delivering a median craniospinal dose of 36 Gy, with an additional boost to the posterior fossa up to 54 Gy. Fifteen patients received chemotherapy. The median follow-up was 62 months (range, 3-213 months). The 5-year, 10-year, overall, and disease-free survival rates were 63%, 51%, 66%, and 55%, respectively. Univariate analysis revealed that hydrocephalus, initial local recurrence, subtotal resection in primary surgery, initial Karnofsky performance status <= 70, duration of symptoms shorter than 30 days, and primary site dose < 54 Gy were found to be negative prognostic factors. Toxicity was moderate. The main therapy in adult medulloblatoms is craniospinal irradiation following surgery. The prognostic factors and outcomes of the patients in our study are concordant with previous reports in the literature.