The aim of this study is to evaluate the effect of an external nasal dilator in patients with nasal obstruction secondary to mucosal congestion (n = 33) or to septal deviation in the nasal valve area (n = 28). A group of subjects with healthy nasal cavities was tested also (n = 51). Acoustic rhinometric and rhinomanometric nasal measurements were performed with and without the dilator and before and after topical decongestion of the nasal mucosa. A visual analog scale was employed to evaluate the subjective sensation of nasal obstruction. Objective measurements showed that the external dilator increased the minimum cross-sectional area and decreased the nasal resistance significantly in all three groups (P < 0.01). The effect was more impressive in patients with septal deviation (P < 0.001). Subjective assessments reflected patency in all subjects except those in the mucosal swelling group (P = 0.06). From this study the authors conclude that the external nasal dilator offers an effective, nonsurgical therapeutic approach in the management of septal deviation that obstructs the nasal valve area. Although patients with nasal obstruction secondary to mucosal congestion showed objective improvement with the nasal dilator, these changes were not accompanied by a sensation of enhanced patency.