Primary cerebellar glioblastomas are exceedingly rare in childhood, with only 19 cases having been reported. We treated a 7-year-old girl with primary cerebellar glioblastoma, who rapidly deteriorated due to cerebrospinal fluid dissemination. The 7-year-old girl was admitted to our hospital with a history of headache for one month. On admission, increased intracranial pressure and left cerebellar signs were observed. Magnetic resonance imaging (MRI) revealed a ring-enhanced mass in the left cerebellar hemisphere and a low intensity lesion in the pons. The tumor had compressed the fourth ventricle and caused obstructive hydrocephalus. Gross total resection of the left cerebellar tumor was performed. Histological examination revealed nuclear atypia, mitoses, and necrosis, which satisfied the World Health Organizations histological criteria for grade IV astrocytoma. The MIB-1 labeling index was more than 60%. She was treated with adjuvant therapies consisting of 60.2 Gy local irradiation to the posterior fossa, including the brain stem lesion, and chemotherapy using 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosourea (ACNU). However, the patient developed of anorexia and vomiting 4 months after surgery, and MRI disclosed local recurrence at the left middle cerebellar peduncle and diffuse dissemination along the lateral ventricle wall. The patient was treated with three-drug chemotherapy using ifosfamide, cisplatin, and etoposide and 39.2 Gy of whole-brain irradiation. However, her condition deteriorated gradually and she died 10 months after admission (6 months after the onset of tumor recurrence). Primary cerebellar glioblastomas in children carry a very poor prognosis and tend to cause cerebrospinal fluid dissemination.