Our goal was to evaluate the influence of the scan parameters on the 3D virtual endoscopy of the larynx and trachea and the clinical assessment. Helical CT (HiSpeed Advantage; GE, Milwaukee, WI, U.S.A.) of a cadaver phantom was performed with increased collimation (1-10 mm) and pitch (0.5-3). Seventy-two patients with complaints of the upper airways were investigated by virtual endoscopy and their results were compared with the findings of regular endoscopy. Best correlation between virtual endoscopy and anatomical findings, diagnostic quality of the axial slices, and useful longitudinal coverage of the examination were obtained with a collimation of 3 mm and a pitch of 1.5. Space-occupying tumors and stenosis were detected correctly, but the mucous membrane could not be visualized. 3D virtual endoscopy proved to be a valuable method for displaying anatomical structures. For an optimal protocol, a collimation of 3 mm with a pitch of 1.5 is recommended.