We found malignant tumor cells in the lumbar cerebrospinal fluid of a 6-year-old girl, whose initial symptoms were raised intracranial pressure and we tried to seek the origin in and out the central nervous system but we failed. After putting a ventriculoperitoneal shunt, we injected anticancer drugs intrathecally, then the patient got better for several months, but 6 months later, she got worse and the contrast-enhanced CT showed a conspicuous pattern of meningeal spread which was a diffuse enhancement of the subarachnoid space from the upper cervical area to the cerebellar folia, basal cistern and the cerebral surface. By surgical management, we diagnosed this to be an undifferentiated type of malignant lymphoma, immunohistologically, Null-cell type, and then we added radiation therapy combined with chemotherapy but there were no improvement of quadriplegia and dyspnea and she expired 10 months later. We reported a case of childhood primary intracranial malignant lymphoma, which proved to be an undifferentiated type and a Null-cell type and whose CT showed characteristic meningeal spread.