To characterize otologic causes for vertigo, data on 564 patients with the six most common diseases involving vertigo were retrieved from the database of a computer-aided diagnostic system for neurotologic diseases. The diseases were Meniere's disease, vestibular schwannoma, benign paroxysmal positional vertigo, vestibular neuritis, sudden deafness, and traumatic vertigo. The prevalence of tinnitus in the study population was 76%. The most severe forms of vertigo and nausea were found in vestibular neuritis, whereas the most severe case of tinnitus appeared in Meniere's disease. Of the patients with vestibular schwannoma, 49% had had vertigo. A linear discrimination analysis using case history classified 90% of the patients into correct groups. The key questions discriminating between the diseases concerned the frequency and duration of vertigo attacks, the duration of hearing loss and vertigo, and the occurrence of head injury. Making a correct diagnosis during the first office visit can be difficult, especially for sudden deafness, vestibular schwannoma, and Meniere's disease. Neurotologic and audiometric information was of minor value in distinguishing between these six diseases. Vestibular schwannoma had significantly greater asymmetry in electronystagmography and smaller gains in smooth pursuit in comparison with the other disease. Factorial analysis did not aid the clustering of these diseases.