ENT-flexible endoscopes are an important tool for ear, nose and throat (ENT) professionals to examine the upper airway. Although image quality has improved significantly in the past decade, there is no generally accepted approach to measure this objectively. Sharpness, visual noise and color fidelity are aspects of image quality that can objectively be measured. The purpose of this study was to explore the relationship between these quality metrics and the subjective perception of image quality by ENT-professionals. The image quality of six different flexible endoscopes was assessed objectively and subjectively. Objective measurements were obtained using the Rez Checker Target Nano Matte and comprised sharpness (MTF50), visual noise and color fidelity (CIE ΔE 2000). Subjective image quality ranking was obtained by presenting images of a single larynx to 30 ENT-professionals in a forced pairwise comparison and asking them to select the image with the best image quality. Differences in image quality between endoscopes are reliably detected by objective measurement and subjective assessment. A strong positive correlation was found between sharpness and subjective ranking (p < 0.005). Visual noise and color fidelity may be relevant, but did not correlate with the subjective assessment and were probably overshadowed by the strong correlation between sharpness and subjective ranking in the data. The authors found that number of pixels on screen to display the registered image differs per type of endoscope, however more pixels do not necessarily imply a sharper image. The authors will continue their investigation of image quality metrics and their relation to diagnostic accuracy which can provide feedback on design and manufacturing optimization to the industry.