A medical disorder in which the septum is deviated. This means that the septum is more to one side than the other. Thus one nasal cavity is bigger than the other. It may cause an actual distortion in the physical shape of the nose, or may not.

A deviated septum sometimes has no effect on the individual's life at all, or the symptoms may appear at some stage in the individual's life. If it is deviated enough to cause an obstruction in one of the nasal cavities, this will usually cause difficulty in breathing. A deviated septum is a prominant cause of PND (Post Nasal Drip), in which the nose produces excess mucus, which trickles down the throat. It is felt as congestion in the throat, but is otherwise mostly harmless.