Hemophagocytic lymphohistiocytosis (HLH) is a rare disease with rarer neurological presentation. When this occurs, diagnosis may be delayed. This report aims to call attention to clinical, laboratory, and radiological features that should prompt the correct diagnosis. A 13-year-old girl presented with progressive increase in intracranial pressure and ataxia. MRI showed a diffuse tumor-like swelling of the cerebellum with tonsillar herniation and patchy white matter post-contrast enhancement. Regression of swelling with steroids ruled out glioma and medulloblastoma, and brain lymphoma was considered. Diagnosis of HLH was reached 2 months after onset when uncontrolled fever and severe elevation of liver enzymes occurred. Two bone marrow biopsies were needed to demonstrate hemophagocytosis. Familial HLH was confirmed by perforin gene mutations. Bone marrow transplantation was performed. The early diagnosis of HLH may be life saving. Awareness of the disease is necessary to investigate its characteristic findings, thus avoiding a delay in diagnosis.