A 5-year-old boy presented with a 1-year history of frontal headache and nausea. Neurological examination showed left abducens nerve palsy, left facial nerve palsy, Bruns'' nystagmus, and wide-based gait. Neuroimaging demonstrated a lesion with moderate linear enhancement in the left cerebellar hemisphere. He underwent stereotactic needle biopsy. The histological diagnosis was well-differentiated small lymphocytic type of malignant lymphoma. Following the biopsy, the patient underwent radiotherapy (whole brain 30 Gy, local 20 Gy). He has been in good condition for more than 5 years. The long-term survival is attributable to the absence of aggressiveness and the good response to radiation of this subtype of malignant lymphoma.