Inner ear DCS manifests with vestibular symptoms (vertigo, nausea, vomiting, ataxia) or cochlear symptoms (tinnitus, deafness) or both. Two distinct patterns of evolution are recognized. The first occurs during decompression from deep dives while the diver is still submerged, and it may be aggravated by a switch from a helium-based breathing gas to a nitrogen-based breathing gas. This is particularly dangerous because it can incapacitate the diver at a time when he or she still has hours of decompression to complete, thus forcing an early ascent with substantial missed decompression. The second occurs after arrival at the surface from more typical recreational air dives, although usually involving moderate depth exposure (greater than 25 metres). In this setting the onset is typically seen within the first 30 minutes of the dive. These different presentations probably have a different pathophysiological basis (see Chapter 10). Both may resolve spontaneously, but they are responsive to recompression and hyperbaric oxygen. Whether treated or untreated, it is certainly possible that long-term injury can follow inner ear DCS. In particular, permanent loss of hearing may occur. Although the vestibular apparatus may be permanently damaged, this does not usually result in long-term symptoms. There is a well-recognized ability for the brain to accommodate asymmetrical vestibular function that takes place over weeks to months and usually results in spontaneous resolution of vertigo and ataxia.