Purpose To perform endoscopic sinus surgery safely and effectively, surgeons need to visualize the complex anatomy of the anterior ethmoid and frontal sinus region. Because this anatomy is so variable and individualized, the foundation of understanding lies in identifying, following, and visualizing the drainage pathway patterns and anticipating possible variations. Methods We studied 100 sides (50 cases: 22 male, 28 female, aged 12–86, average age 46.5 years, ± 19.5) using computed tomography (CT) and multiplanar reconstruction (MPR) to identify and classify the drainage pathways leading to the frontal sinus and anterior ethmoidal cells. Results Analysis revealed five patterns of drainage pathways defined by their bony walls: between the uncinate process and the lamina papyracea [UP–LP]; between the uncinate process and the middle turbinate [UP–MT]; between the uncinate process and the accessory uncinate process [UP–UPa]; between the uncinate process and the basal lamella of the ethmoidal bulla [UP–BLEB]; and between the basal lamella of the ethmoidal bulla and the basal lamella of the middle turbinate [BLEB–BLMT]. In most cases, BLEB formed the posterior wall of the drainage pathway of the frontal sinus, indicating BLEB could be one of the most important landmarks for approaching the frontal sinus. Conclusions As endoscopic sinus surgery depends on an understanding of this anatomy, this study may help surgeons to identify and follow the drainage pathways more accurately and safely through the anterior ethmoid to the frontal sinus.