Prospective and retrospective morphometric CT (axial and coronal) research was performed with 100 healthy persons and 163 patients (145 males, 118 females, mean age 50 years, range 1-88 years). The patients were classified into the following groups: chronic sinusitis (n = 85), polyposis (n = 25), mucoceles (n = 13), benign tumors (n = 20) and malignant tumors (n = 20). After initial calibration with the scale (in cm) displayed on the CT image, each paranasal sinus was outlined following its bone inner surface. The data were processed with a high-resolution analysis system, and volumes were calculated using an integration areas rule. The ethmoid, maxillary and sphenoid sinuses exhibited an increase in volume for a period of up to 15 years, afterwards maintaining similar values. The frontal sinus grows in a monomodal pattern (peak at 30 years). The volumetric results (mean and standard deviation) in the normal adult group were as follows: maxillary sinus 13.07 cm3 (6.8), ethmoid 5.5 cm3 (2.0), sphenoid 3.5 cm3 (2.6) and frontal 3.7 cm3 (3.6). Primary frontal and maxillary sinus hypoplasia appeared in 3.9% and 1.3% of cases, respectively. The anatomic variations were as follows: concha bullosa 8.3%, Haller cells 3.2% and Onodi cells 8.3%. The sinusitis values (adults) were greater than those in the normal group: 14.4 cm3 (7.3), 6.8 cm3 (2.9), 2.9 cm3 (1.9) and 4.2 cm3 (5.2), with the exception of the sphenoid, but the difference was not statistically significant. Finally, we propose a new classification for paranasal sinus tumors (benign and malignant), volumetric T (vT), taking into account the morphometric tumoral volume and the mean volumetric value of normal sinuses.