Coronal plane computerized tomographic (CT) scanning has dramatically improved the imaging of paranasal sinus anatomy as compared to sinus radiographs. Increasingly, subtle bony anatomic variations and mucosal abnormalities of this region are being detected. Data regarding the "background" prevalence of these findings are needed to determine their clinical relevance. A detailed analysis of coronal plane CT scans of the paranasal sinuses obtained in 202 consecutively imaged patients was conducted. Special attention was directed toward identifying bony anatomic variations and mucosal abnormalities. Anatomic variations studied included pneumatization of the middle turbinate, paradoxical curvature of the middle turbinate, Haller's cells, and pneumatization of the uncinate process. Such bony anatomic variations were detected in 131 (64.9%) of 202 patients and were found with a similar frequency in patients scanned for sinus complaints and in those scanned for nonsinus reasons. Mucosal abnormalities were detected in 168 (83.2%) of 202 patients. For those patients scanned during the evaluation of sinus-like complaints, mucosal abnormalities were noted in 153 (92.2%) of 166 cases, and were predominantly detected in the anterior ethmoid region. For patients scanned during nonsinus evaluations, mucosal abnormalities were detected in 15 (41.7%) of 36 cases, without predilection for the anterior ethmoid region. Discussion regarding the prevalence and clinical significance of paranasal sinus bony anatomic variations and mucosal abnormalities is included as a guide to assist the otolaryngologist and/or radiologist in the evaluation of coronal sinus CT scans.