We report on a 70-year-old male who developed cavernous sinus syndrome as the initial symptom of multiple myeloma. He was admitted with diplopia and ptosis in October 2004. The diagnosis of multiple myeloma and cavernous sinus syndrome due to a gross mass at the sinus base were made. Cerebral computed tomography revealed that the lesion occupied the sphenoid sinus and involved the oculomoter nerve. He underwent local irradiation of the mass followed by systemic chemotherapy. The symptoms caused by the mass disappeared after the treatment. Clinicians need to be aware of the rare manifestation of multiple myeloma.