In patients with chronic rhinosinusitis, the presence of maxillary sinus hypoplasia (MSH) may be obscured by extensive mucosal disease or nasal polyposis. Recognition of MSH and its effect on adjacent anatomic structures is of utmost clinical significance in endoscopic sinus surgery. Failure to recognize the impact that MSH has on the position of the ethmoid infundibulum relative to the medial orbital wall could lead to inadvertent damage to the wall during surgery. We conducted a prospective study of 75 patients with clinically and endoscopically proven chronic rhinosinusitis to evaluate the prevalence of MSH. We found that MSH was present in 12 patients (16.0%); 7 of the 75 patients (9.3%) had bilateral disease, and 5 (6.7%) had unilateral disease. We then correlated the relationship of the ethmoid infundibulum to the medial orbital wall as determined by computed tomography in patients with and without MSH. We found that in most cases of MSH, the ethmoid infundibulum was displaced lateral to the medial wall of the orbit; the correlation between MSH status and displacement was statistically significant (p < 0.05). We propose the term “infundibular lateralization” to describe this consistent radiologic finding in MSH.