Vertigo is relatively common after diving. Although it may be the result of the changes in pressure, it can also be a feature of decompression accidents, of clinical toxicity, simply be a manifestation of altered physiology resulting from immersion in a weightless environment in which all the organs involved in maintaining equilibrium (vestibular system, proprioception and vision) are affected. It seemed to us to be of interest to study the incidence of vertigo in naval divers by means of an anonymous questionnaire. The responses were elicited over a 3 month period from 333 divers. 45 divers reported clinical sensations of vertigo, an incidence of 13.5%. If this figure is related to the number of dives, the incidence falls to 0.06%. No decompression accidents were reported. The main aetiology was barotrauma, 42% being of alternobaric and 36% of pressure type. The remaining aetiologies were sensory illusions in 6% of cases, and other non-ENT causes in 16%. After a review of the physiopatholgy and study of the case hisotries, there is a discussion of the features which allow the aetiology to be determined and treatment planned.