The frontal cell is a rare anatomic anomaly that can become the etiology of chronic frontal sinusitis. It is an anterior ethmoid cell that can be differentiated from other ethmoid cells by serial analysis of sinus CT scans. Located cephalad to the middle meatus, it may obstruct natural mucociliary clearance by impinging on the frontal recess or the frontal sinus cavity. A classification of 4 types frontal cell (Type I-IV) is described. This anatomy is demonstrated in radiographic images of cadaver and patient sinuses. Four consecutive clinical cases of frontal cell obstruction of the frontal sinus are reviewed. In three instances, we performed a combined external and endoscopic intranasal frontal sinusotomy to effectively relieve the obstruction. We describe this technique in detail and provide a mean follow-up of 6 months for these four patients. With recognition of frontal cell obstruction of the frontal sinus, and proper treatment, the results appear to be very rewarding.