A 67-year-old man presented with progressive diplopia. On evaluation, he was noted to have bilateral palsies of cranial nerves III, IV and VI as well as a unilateral right true vocal fold paralysis. CT and MRI studies demonstrated a T2-bright left ethmoid mass with no evidence of bony erosion. Direct visualisation demonstrated a polypoid appearing mass of the left sphenoethmoid recess. Operative biopsy was pursued with final pathology demonstrating benign seromucinous hamartoma. Subsequent blood work demonstrated high titres of anti-acetylcholine receptor antibodies consistent with myasthenia gravis. The patient was started on pyridostigmine with improvement in his ocular cranial neuropathies.