It is well known that paroxysmal positional vertigo is induced by change of head position and subsides immediately when the head is returned to the original position. There are two types of paroxysmal positional vertigo. One is what DIX and HALLPIKE (1952) call the benign type which is thought to be caused by otolith lesions. Another is a malignant type, in contrast to the former and is related to a lesion in the central nervous system. Otologists are usually familiar with the former, but the latter is not known among neurologists and neurosurgeons. We experienced 37 cases of the malignant type and found that this type of paroxysmal vertigo is induced by various diseases. Furthermore, we believe that the mechanism of this paroxysmal vertigo is the lack of inhibitory function of the vestibular cerebellum, and not abrupt malfunction of communication of the cerebrospinal fluid in the ventricular system. We also believe that this symptom is a very useful sign for diagnosing lesions of the cerebellar vermis.