The purpose of this study is to evaluate multislice spiral CT (MSCT) in multiplanar functional imaging of the larynx and hypopharynx and to define the optimal image planes for the delineation of the tumor and specific anatomical structures. Forty patients with suspected tumors of the larynx or hypopharynx were examined with MSCT during quiet breathing (QB), E-phonation (EP) and modified Valsalva maneuver (VM). Images were read in the axial, coronal and sagittal planes. Overall image quality, delineation of the tumor and anatomic structures for different conditions and orientations were graded using a three-point scale; the conditional permutation test was applied to detect quality differences. Differences between image types were statistically significant. The axial plane was superior in overall image quality and the delineation of the tumor, pyriform sinus, vocal cords and fat within the parapharyngeal/visceral space. The coronal plane was best for delineating the ventricle and the paraglottic space, the sagittal plane for the retropharyngeal and the preepiglottic space. For tumor detection, sensitivity, specificity and accuracy were 0.92, 1.0 and 0.93 for QB.ax, 0.94, 0.8 and 0.92 for EP.ax and 0.85, 1.0 and 0.87 for VM.ax, respectively. Examination during QB should be the standard procedure; additional scanning with EP improved tumor assessment.