The most studied recess of the sphenoid sinus seems to be the lateral one, which is highly variable. Less attention seems to be paid to the maxillary recess, extending anterior, inferior and lateral towards the maxillary sinus. Twenty patients were referred for CT of the paranasal sinuses (axial CT), during a 3-month period. After examining the morphology of the sphenoid sinuses, the authors found bilateral maxillary recesses in one patient. On either side, the maxillary recess of the sphenoid sinus was directed anterior and lateral, being separated from the maxillary sinus by a distinctive bony wall; the longitudinal size of these recesses was 1.36 cm, on the left, and 1.22 cm, on the right. As it becomes part of the antero-medial wall of the pterygopalatine fossa, the maxillary recess of the sphenoid sinus should be evaluated prior to the endoscopic endonasal approach of the fossa; the detail becomes more relevant when one takes into account the fact that in our case, on the right side, the CT-scan suggested that the sphenopalatine artery could traverse directly through the maxillary recess. Therefore, such a maxillary recess of the sphenoid sinus seems to be anatomically located in the situs of the orbital process of the palatine bone and thus, it assumes the respective topography. The differential diagnosis with a Haller cell is relevant--the surgical procedures that approach a Haller cell could lead to a misdiagnosed maxillary recess of the sphenoid sinus into the middle nasal meatus. This aspect determined us to consider the maxillary recess of the sphenoid sinus as a false Haller cell and to claim the imperative of a CT-evaluation performed prior to interventions.