Objectives/Hypothesis The anatomy of the posterior glottis, specifically the states of the posterior glottis during phonation, has not been thoroughly explored in laryngology. Conventional wisdom about the posterior glottis indicates that it tends to be completely closed in men but may be open in women. Furthermore, professional singers are expected to have a completely closed posterior glottis. The aim of this study was to investigate whether these generalizations are true by comparing rigid videolaryngostroboscopy results with high‐resolution computed tomography (HRCT) and three‐dimensional (3D) reconstruction findings. Study Design Prospective study. Methods Of the 90 volunteers (58 women, 32 men) examined, 48 were female professional singers, 10 were female nonsingers, 22 were male professional singers, and 10 were male nonsingers. Rigid videolaryngostroboscopy as well as HRCT scans were performed during singing at the average singing fundamental frequency. HRCT images of the larynx and air‐column were 3D visualized using the software MIMICS®. The states of the posterior glottis were assessed in both examinations and compared among participants. Results The sensitivity of endoscopy was 67.5%. Complete closure of the posterior glottis was observed in 62.5% men and 52% women ( P = .33). Complete closure of the posterior glottis was observed in 35% nonsingers and 61% professional singers ( P = .036). Conclusions The closure of the posterior glottis seen on videolaryngostroboscopy does not always correlate with actual closure. There seems to be no link between sex and complete closure of the glottis. However, there is strong evidence that posterior glottis closure can be influenced, to some degree, by vocal training. Level of Evidence 4 Laryngoscope , 132:124–129, 2022