We introduce acoustic rhinometry as a new, objective method to assess the geometry of the nasal cavity. The cross-sectional area of the nasal cavity as a function of distance from the nostrils was obtained. A group of 21 patients with septal deformities was examined with acoustic rhinometry preoperatively and postoperatively. These values were compared with those of 21 normal control subjects. The minimal cross-sectional area (MCA) is located in the anterior part of the nose, and it shifts anteriorly under the effect of decongestion. The preoperative value of MCA is related to the location and severity of the anterior septal deformity. Postoperative smaller MCA found in the opposite side of that narrowed by a severe anterior septal deformity may be explained by the impact of septoplasty without reduction of a hypertrophic turbinate. A highly significant relation between MCA and the subjective feeling of nasal patency, before and after surgery, suggests that MCA is a valuable parameter to express nasal patency. Correction of posterior septal deformities is found to increase significantly the cross-sectional area posteriorly. The effect of decongestion in the postoperative values, however, suggests that the mucosa contributes even more to the cross-sectional area of the posterior part of the nose. Acoustic rhinometry seems very suitable for evaluation of the nasal cavity in cases where septoplasty and turbinoplasty is considered, as well as for the postoperative evaluation.