Holmes-Adie syndrome, or tonic pupil syndrome, is a condition characterized by a triad of main symptoms: unilateral tonic pupil dilation, accommodative paresis without or with a significant reduction in pupillary light reflex, and decreased tendon reflexes. The disease is based on dysfunction of the parasympathetic nervous system. The syndrome results from damage to the ciliary ganglion, which carries parasympathetic innervation to the m.sphincter pupillae, cornea, and eyeball. Often the condition is accompanied by dysfunction of the spinal ganglia and, as a consequence, autonomic dysfunction in the form of sweating disorders, usually on one side of the body, rarely — by heart rhythm disorders, lability of blood pressure. A frequent sign of Adie syndrome is the absence or reduction in patellar, rarely Achilles, reflexes. The etiology of the disease is not definitively determined, bacterial or viral factors are not excluded. The diagnosis of Adie syndrome is mainly based on a clinical comparison of the symptoms of the disease, as well as on a thorough and comprehensive examination by a neuroophthalmologist with mandatory testing of pupillary responses with low doses of pilocarpine (narrowing of the pupil is characteristic). Despite the positive prognosis for the patient’s life and his ability to work, the condition belongs to the group of difficult-to-treat ones, and the management consists in symptomatic vision correction.