BACKGROUND Retrograde cerebral perfusion (RCP) was clinically introduced as a supportive technique to protect the brain during operations on the thoracic aorta. However, it remains unclear whether this procedure provides adequate blood supply for the brain. METHODS We have observed the optic fundus of patients undergoing operation on the thoracic aorta to evaluate the cerebral circulation during RCP. There were 1 male and 3 female patients, ages ranged from 34 to 78 years. RCP time ranged from 39 to 70 minutes, and blood flow via the superior vena cava cannula ranged from 200 to 400 ml/min. RESULTS The arteries of the retina showed marked constrictions soon after the initiation of RCP. The veins showed almost normal diameter. The large arteries were reduced to thin threads, while the smaller arteries were invisible at 30 minutes after the initiation of retrograde cerebral perfusion. CONCLUSIONS Ophthalmoscopic findings demonstrate the reduction of cerebral blood flow, especially in arteries, during RCP. Although RCP is a useful technique for cerebral protection, it could be mentioned that the blood supply to the brain by RCP is not enough to maintain good cerebral metabolism.