Twenty ethmoidal mucoceles were treated and observed for a minimum of two years after surgery. Unilateral exophthalmos was the initial complaint in all cases and nasal polyposis was a noteworthy finding in more than half of the patients. The lesions always extended into the orbit and usually eroded the floor of the frontal sinus. Exenteration through an ethmoidectomy approach was successful in 16 cases. Failure was due to recurrence of the mucocele in one case and in three cases to uncontrolled polypoid disease that produced recurrence of the exophthalmos. Long-term follow-up is mandatory since recurrences may take several years to occur.