Background: Although extensive research has been conducted on paranasal sinuses across various human populations and animal species, studies focusing on dogs remain relatively scarce. Purpose: This study aimed to characterise the anatomical and morphometric structure of canine paranasal sinuses utilising computed tomography (CT) cross-sectional imaging and three-dimensional (3D) reformatted models. Methods: In this study, CT images of 14 clinically normal dogs (7 females, 7 males) with a mean age of 6.2 ± 4.3 years were analysed. The localisation and boundaries of the paranasal sinuses, as well as the orientation and morphology of sinonasal openings, were identified through cross-sectional imaging, whereas morphometric characteristics were evaluated using 3D models. Results: Despite variations in shape among all examined animals, the paranasal sinuses bilaterally consisted of maxillary recess (MR) and frontal sinus (FS) (rostral, medial and lateral). In one 4-year-old male, the rostral FS was absent. The MR exhibited a volume of 4 cm³ and a surface area of 26 cm². The lateral FS was the largest, accounting for 90% of total sinus volume and 78% of total surface area in both sexes, whereas the medial FS was the smallest, with respective ratios of 3% and 8%. The MR was identified as the most symmetrically positioned sinus, whereas the medial FS displayed the highest degree of asymmetry. In females, the right lateral FS had a significantly larger surface area than the left. No correlation was found between age and sinus morphometry. Conclusion: Although this study was conducted on animals of certain age and sex, without considering breed-specific characteristics, the findings contribute to a more detailed understanding of the cross-sectional and reconstructive anatomy of the region. Moreover, these preliminary reference data may aid radiologists and clinicians in diagnosing sinonasal diseases.