The bony septum ossifies from cranial to caudal and from ventral to dorsal, thereby forming the perpendicular plate of ethmoid bone and vomer. A small strip of cartilage from the cartilaginous septum remains between these parts, the so-called sphenoidal process of the cartilaginous septum. This sphenoidal process is usually seen at the top of a deviated nasal septum during septoplasty. This study evaluated the clinical significance of the sphenoidal process of the cartilaginous septum as a cause of nasal septal deviation. We studied 37 patients with septal deviation who underwent septoplasty. The complex consisting of the sphenoidal process of the cartilaginous septum, perpendicular plate of the ethmoid bone (PPE), and vomer was removed at surgery. The sphenoidal process was measured and the surgical specimen were evaluated histologically and compared to controls. The mean length of the sphenoidal process in patients with a deviated nasal septum was 26.05 +/- 5.32 mm versus 11.95 +/- 2.38 mm in controls. The sphenoidal process was significantly longer in the patients with a deviated nasal septum (P < 0.05). The sphenoidal process of the cartilaginous septum was connected to the PPE and vomer in the patients with a deviated nasal septum and differed histologically from that of the controls. The sphenoidal process of the cartilaginous septum was long and prominent in the patients with septal deviation, implying that delayed nasal septal ossification may be one cause of nasal septal deviation.