Meningeal carcinomatosis （MC） is a disease of malignant tumor dissemination or invasion in the leptomeninges/meninges and the subarachnoid space without the involvement of brain parenchyma， and it is a rare type of metastatic tumor of the central nervous system and has an extremely low incidence rate in patients with solid tumor. MC often has an insidious onset and displays complex but non-specific symptoms， and patients may have the manifestations of headache， change in consciousness， and various neurological defects， which may lead to misdiagnosis and missed diagnosis in patients with unknown primary lesions and encephalopathy as the initial symptom. This article analyzes the clinical data of a patient with the initial manifestation of leptomeningeal metastasis and the primary lesion of colonic adenocarcinoma， in order to improve the awareness of this disease.