Maxillary sinus hypoplasia is an anomaly of the paranasal sinuses occasionally encountered by otolaryngologists. Although this entity has been previously reported, an association between maxillary sinus hypoplasia and anomalies of other paranasal sinus structures, such as the uncinate process, has not yet been described. Additionally, the literature lacks a system by which the various types of maxillary sinus hypoplasia can be classified using computerized tomographic (CT) imaging. Two hundred and two consecutive coronal sinus computerized tomographic scans from patients undergoing evaluation at our institution were analyzed to determine the prevalence of MSH and associated paranasal sinus anomalies. The overall prevalence of maxillary sinus hypoplasia was 10.4%. Three distinct patterns of hypoplasia were evident. Type I, characterized by a normal uncinate process, a well-defined infundibular passage, and mild sinus hypoplasia, occurred in 14 patients (6.9%). Type II, characterized by absence or hypoplasia of the uncinate process, an ill-defined infundibular passage, and soft-tissue density opacification of a significantly hypoplastic sinus occurred in 6 patients (3.0%). Type III, characterized by absence of the uncinate process and a profoundly hypoplastic, cleft-like sinus, occurred in 1 patient (0.5%). Recognition of associated anomalies of the uncinate process in patients with maxillary sinus hypoplasia undergoing sinus surgery is of utmost clinical significance because the uncinate process serves as a key landmark during functional endoscopic sinus surgery. Failure to recognize hypoplasia or absence of the uncinate process could lead to inadvertent intraoperative damage to the adjacent medial orbital wall.