BACKGROUND AND PURPOSE: Recent interest in the origin and complications associated with frontal intersinus septal cells prompted us to review our material looking for cases of the uncommon occurrence of a mucocele developing within such a cell. The purpose of this article was to present the imaging findings on 4 cases of mucoceles arising within surgically proven frontal intersinus septal cells. MATERIALS AND METHODS: A retrospective review of the case material in our department of otolaryngology since 2000 was made looking for cases of patients with surgically proven frontal intersinus septal cell mucoceles. Institutional review board approval for the review was obtained. Four cases were identified that also had CT and/or MR imaging studies. Examples of 4 additional classic frontal sinus mucoceles and 3 anterior ethmoid mucoceles were also identified for comparison. RESULTS: All 4 of the cases of frontal intersinus septal cell mucoceles had an expanded midline frontal sinus cell, which thinned the posterior and/or anterior frontal sinus tables. The classic frontal sinus mucoceles were either to the left or right side, and any table thinning was off midline. The ethmoid mucoceles were clearly centered below the frontal sinuses. CONCLUSIONS: The rare occurrence of a frontal intersinus septal mucocele can be diagnosed on CT and MR imaging studies, because its appearance in the midline is clearly distinct from the more common classic frontal sinus mucoceles that develop within the left or right frontal sinus proper. Distinction is also routinely made from large anterior ethmoid mucoceles.