Abstract: Background　Diffuse meningeal melanocytic hyperplasia (DLM) is a rare, well-differentiated malignant or borderline tumor. It is more common in children, and even rarer in adults.Objective　To report a case of DLM in the brain and provide reference for clinical diagnosis and treatment. Methods　Clinical data about a patient with intracranial primary diffuse meningeal melanocytic hyperplasia who visited to the Emergency Department of the First Medical Center of Chinese PLA General Hospital on July 12, 2018 were retrospectively analyzed, and the relevant literatures were reviewed.Results　The patient was a 21 year-old male who initially presented with seizures and signs of increased intracranial pressure. A plain cranial MRI showed no abnormalities; however, the contrast-enhanced MRI revealed sheet-like enhancement along the cerebral sulci, with localized thickening and enhancement of the meninges, and notable thickening and enhancement of the bilateral cavernous sinuses. The case was initially misdiagnosed as venous sinus thrombosis and viral encephalitis. Subsequently, the patient underwent a lateral ventricular-peritoneal shunt and intracranial lesion biopsy, with the pathological diagnosis confirming DLM. Following 30 sessions of whole-brain radiotherapy, the patient had a survival period of 4 years.Conclusion　DLM exhibits varying MRI manifestations due to differences in melanin content, which may lead to misdiagnosis. Definitive diagnosis relies on pathological examination. Key strategies for improving prognosis include early and accurate diagnosis, maximal resection of lesions during surgery, adjuvant radiotherapy and chemotherapy, and immunotherapy.