Mucoceles of the sphenoid or posterior ethmoid sinuses usually behave in a similar manner. Because of the thinness of surrounding bone and the proximity of vital structures, these lesions can expand aggressively at a clinically alarming rate. Presenting symptoms vary but characteristically include headache and ocular disturbance. Careful radiologic evaluation helps in the correct assessment of these lesions. The authors feel that the rhinologic approach to the sphenoid cavity, via an external ethmoidotomy, affords the best visualization possible of the diseased area without entailing possibly serious central nervous system complications. Six cases are discussed from the standpoint of pi’esenting signs and symptoms, radiologic assessment, therapy and outcome.