Meningeal carcinomatosis is a well-known complication of malignant neoplasms. We report a case of meningeal carcinomatosis of 2 months' duration in a 22-year-old man, in whom the initial symptom was gradually worsening headache. Postmortem examination revealed infiltrating adenocarcinoma of the stomach. Carcinoma cells showed diffuse spread to the subarachnoid space of the brain and spinal cord. In many places, subarachnoid tumor cells had infiltrated to the cranial and spinal nerves. Moreover, carcinoma cells in the nerve roots extended to the parenchyma of the brain and spinal cord beyond the CNS-peripheral nervous system junction. These findings suggest that cranial and spinal nerve roots can be a possible route of parenchymal invasion in meningeal carcinomatosis.