The absence of a maxillary or sphenoid sinus in an adult is an extremely rare condition. We investigated maxillary and sphenoid sinus aplasia in adult Turkish individuals using computed tomography (CT). We examined CT scans in the axial and coronal planes of the paranasal sinuses in 1,526 patients. The CT scans of a 21-year-old male were notable for bilateral maxillary sinus aplasia. Another patient, a 20-year-old female, had CT scans that showed the unilateral absence of a maxillary sinus. Two additional cases showed the unilateral absence of one sphenoid sinus. Bilateral absence of the sphenoid sinuses was not observed in our study. The clinical implications of maxillary and sphenoid sinus aplasia will be further discussed. (C) 2004 Wiley-Liss, Inc.