The present investigation was part of a project performed to detect possible effects of diving on the cochleovestibular system. A group of 194 professional divers were interviewed, examined otologically, and their hearing was tested audiometrically. Caloric vestibular tests were performed in 48 subjects. The interview reviewed age, diving experience, previous ear disease or injury, head trauma, noise exposure during diving and during spare-time activities, eye color, tobacco habits, and the occurrence of vertigo during diving. Useful information regarding vertigo was obtained from 193. Of the 76 (39%) who had experienced vertigo, 64 (33%) were classified as alternobaric vertigo (AV), a type of vertigo caused by asymmetric middle ear pressure. A stepwise multiple logistic regression analysis was performed to detect variables contributing to the presence of AV. Variables having a statistically significant association with AV were previous barotrauma of the ear (P less than 0.05) and noise exposure during diving (less than 0.05). AV was most frequently encountered when diving during a common cold. In this sample of divers, AV did not lead to any serious or critical situations.