Thirty patients, primarily diagnosed as having vestibular neuronitis, were investigated with a test battery consisting of neuro-otological, neuro-ophthalmological, neurological examinations and electro-oculography. Initial routine examination failed to reveal involvement of structures outside the vestibular nerve, whereas neurological evaluation and analysis of the cerebrospinal fluid indicated an intrinsic central nervous system (CNS) disorder in 6 cases. The electro-oculographic analysis revealed abnormalities supporting a 'central' cause of the vertigo in 12 cases. Altogether 13 patients showed signs of a possible intrinsic CNS disorder. Consequently, although routine examination may indicate a diagnosis of vestibular neuronitis, the patient concerned frequently has signs of an intrinsic CNS disorder and not a disorder of the peripheral nerve.