It is rare to find vestibular disorders in the course of purulent acute otitis media when simple serous labyrinthitis has been excluded as possible cause. Twelve such cases are presented, in which the symptom is interpreted as an isolated manifestation of acute, non-suppurating encephalitis. It is characterized by the sudden onset, the transitory nature and rapid change of the nystagmus, in which no regular pattern can be discerned, and by the normal sensitivity of the auditory passage to heat and the absence of signs of inner-ear hearing defects. Thrombosis, congestion as a result of damage to the vessel walls by bacterial toxins, with subsequent localized oedema, reflex mechanisms from the diseased focus, vasodilating vagus influence via the superficial petrosus major or an allergic process in the region of the central vestibular nerve pathway are all discussed as possible causes for this generally quite benign condition.