Patients with medulloblastoma frequently present with hydrocephalus. While not all patients with medulloblastoma will continue to suffer from hydrocephalus after tumor resection, there is a significant proportion who will require a permanent shunt. We have retrospectively reviewed a group of children with medulloblastoma not shunted preoperatively, and have identified several characteristics which are associated with a requirement for permanent shunt. We studied 42 patients and found that 17 patients (40%) required permanent shunts within 4 weeks of craniotomy. The shunted patients were younger (5.4 +/- 2.9 vs. 10.0 +/- 5.7 years; p < 0.01), had larger ventricles (p < 0.05), and had more extensive tumors (Chang's stage T3 and T4; p < 0.01). These variables were all independently significant. In addition, we found that the patients requiring postcraniotomy shunts had a much higher rate of morbidity including a postoperative pseudobulbar syndrome. Of interest, we found that none of our patients without the above characteristics required a shunt. In particular, we found that no patient older than 10 years required a shunt. Thus, we conclude that younger patients with moderate to severe preoperative hydrocephalus and extensive tumors may benefit from perioperative CSF diversion. Other patients not meeting the above criteria can probably be safely managed with perioperative corticosteroids alone.