Mucoepidermoid carcinoma of the maxillary sinus is a rare neoplasm. We describe diagnostic difficulties in a case of low grade mucoepidermoid carcinoma of a cystic pattern in a 72-year-old man. The patient complained of double vision and nasal bleeding. CT findings indicated a shadow in the unilateral maxillary sinus as well as bony destruction of the maxilla on the same side. Although biopsies and maxillary operations were repeatedly performed over a period of 7 years, the histopathological diagnoses were chronic sinusitis with necrotic characteristics or squamous cell carcinoma.Several cases of mucoepidermoid carcinoma have been similarly misdiagnosed as squamous cell carcinoma because mucoepidermoid carcinomas contain epidermoid cell components similar to squamous cell carcinomas. Tumor necrosis in our case were extensive and the mucous discharge secreted by mucous cell components in this type of carcinoma may increase pressure inside the cystic tumor causing tumor necrosis. The significance of a differential diagnosis between mucoepidermoid carcinoma and chronic inflammation or squamous cell carcinoma in the maxillary sinus should be emphasized.