Pupil tests provide a convenient and simple method for evaluation of autonomic function. Most patients with autonomic disorders show evidence of sympathetic or parasympathetic deficits in the pupil, and these can be detected using a combination of clinical signs, pupillometric tests (measuring the responses to light, or an accommodative effort, or a sudden noise) and pharmacological tests (using topically applied drugs both to confirm a deficit and to localize the lesion). Caution is needed in the interpretation of these tests, particularly if the deficits are mixed (i.e. sympathetic and parasympathetic) or bilateral. The pattern of autonomic disturbance in the pupils often correlates poorly with autonomic function elsewhere, but may have diagnostic value in discriminating between different underlying conditions.