Objective and Importance: The authors present a rare case of a primary cranial vault lymphoma, mimicking a subacute subdural hematoma after head trauma. Clinical Presentation: A 78-year-old woman was admitted to the hospital with progressive left hemiparesis, headache and a gradually increasing soft lump over the right parietal region 1 week after head trauma due to falling from a high place. A computed tomography (CT) scan demonstrated a hyperdense parieto-occipital subdural and subgaleal lesion together with marked midline shift and white matter edema. Intervention: Considering her trauma story and clinical progression, the patient underwent an emergency operation with the diagnosis of subdural hematoma. However, the lesion was found to be of a tumoros nature and the histopathological diagnosis was high-grade malignant non-Hodgkin's lymphoma. Conclusion: The authors emphasize the rarity of primary cranial vault lymphoma and its importance in the differential diagnosis of cranial vault mass lesions extending either intra- or extracranially. This case may be considered as another example where magnetic resonance imaging (MRI) is the ultimate definitive test in the emergency ward whenever CT demonstrates any findings which are unclear.