To report a case of iatrogenic Horner's syndrome after video-thoracoscopic surgery for primary pneumothorax.

An 18-year-old man with ptosis in the right eye was referred to our clinic. The patient had undergone wedge resection via video-thoracoscopic surgery for primary pneumothorax three weeks previously. On ocular examination, the palpebral fissure width was 7 mm in the right lid and 8 mm in the left lid, the marginal reflex distance 1 (MRD 1) was 2 mm in the right lid and 3 mm in the left lid, and the bilateral levator muscle function was good. Anisocoria was present, and pupil size in a dark room was 2.5 mm in the right eye and 4 mm in the left eye. The patient complained of facial anhidrosis on the right side of the face.

Although iatrogenic Horner's syndrome is rare complication of video-thoracoscopic surgery for primary pneumothorax, diagnosis after surgery of the thoracic cavity should be made carefully.