We report here a 65-year-old man with ptosis, diplopia, and progressive lower limb muscle weakness without nasal symptoms. CA19-9 and CEA were elevated in the serum and cerebrospinal fluid (CSF), but Squamous Cell Carcinoma Antigen (SCC) was not. CA19-9-positive atypical cells were found in the CSF. A right ethmoidal tumor was discovered by paranasal CT and 18F-Deoxyglucose Positron Emission Tomography (FDG-PET) studies. The ethmoidal tumor invaded to the orbits and disseminated into the CSF space through the cribriform plate. Biopsy demonstrated that the paranasal tumor consisted of mucoepidermoid carcinoma. We report here the first case of meningeal carcinomatosis due to mucoepidermoid carcinoma in the ethmoid sinus.