The vestibular system senses the position of the head and body in space, in relation to gravity and movement. This helps the animal maintain balance and coordinate eye movements with movement of the head. The receptors for the vestibular system are located in the inner ear, adjacent to the hearing receptors. Vestibular information is processed in the lower portion of the brain in the brainstem and cerebellum. Therefore a problem in the inner ear or one in the brain can affect the vestibular system. The phrase "vestibular disease" is a general term referring to any abnormality of the vestibular system, although some people use this term to mean idiopathic vestibular disease (see below).

Clinical signs:
Signs of vestibular disease include ataxia, head tilt, and abnormal nystagmus. A wide-based stance and swaying of the head and trunk characterize ataxia. The patient may tend to lean and fall to one side. In severe cases, the animal may continuously roll to one side. Head tilt is an abnormal position of the head such that one ear is held lower than the other. Nystagmus is a rhythmic movement of the eyes, where the eyes move back and forth or up and down. In some cases of vestibular disease, there is a sudden onset of severe signs. This may initially be confused with a seizure.

 Canine idiopathic vestibular syndrome:
This is also a common cause of vestibular disease in the dog. Another name is geriatric vestibular syndrome. Older dogs (mean age 12.5 years) are primarily affected. There is a sudden onset of ataxia (which can be severe), head tilt, nystagmus and occasionally vomiting. The cause of this syndrome is unknown. Diagnosis is based on the signs and excluding other causes of vestibular dysfunction. Affected dogs improve spontaneously within 2 weeks, although there may be a mild, persistent head tilt. Nursing care is important during recovery. Unfortunately, affected dogs are sometimes euthanized because of the severe signs and concerns that the patient has a brain tumor or stroke.