We used pipe models to investigate the effects of paranasal sinus ostium. size and paranasal sinus volume on the area-distance curves derived by acoustic rhinometry (AR). Each model had a Helmholtz resonator or a short neck as a side branch that simulated the paranasal sinus and sinus ostium. The AR-derived cross-sectional areas posterior to the ostium. were significantly overestimated. Sinus volume affected the AR measurements only when the sinus was connected via a relatively large ostium. The experimental area-distance curve posterior to the side branch showed pronounced oscillations in association with low-frequency acoustic resonances in this distal part of the pipe. The experimental results are discussed in terms of theoretically calculated "sound-power reflection coefficients" for the pipe models used. The results indicate that the effects of paranasal sinuses and low-frequency acoustic resonances in the posterior part of the nasal cavity are not accounted for in the current AR algorithms. AR does not provide reliable information about sinus ostium size, sinus volume, or cross-sectional area in the distal parts of nasal cavity.