Meningeal carcinomatosis (MC) is a kind of disease in which malignant tumor spreads or infiltrates the soft brain (spinal) membrane and subarachnoid space, but leaves the brain parenchyma uninvolved. It is a rare type of metastases of the central nervous system and shows a low incidence in solid tumor patients. With a hidden onset, MC usually displays complicated but non-specific symptoms. Patients may present with headache, consciousness change and various neurological defects. For patients with unclear primary focus and encephalopathy as the initial symptom, it is easy to be missed or wrongly diagnosed. This article analyzes the clinical data of a patient with meningeal metastasis as the primary manifestation of colorectal adenocarcinoma, in order to improve the vigilance and understanding of this disease.