Continuous retrograde cerebral perfusion (CRCP) during hypothermic circulatory arrest is a useful adjunct for brain protection during aortic arch surgery. According to our experience, no correlation was observed between perfusion pressure and flow rate. Internal jugular vein valves can restrict the flow of CRCP. We performed a study of internal jugular valves, morphologically in autopsy specimens and functionally in clinical patients. Apparently good venous valves were observed in 18 out of 30 cases (60%) on the right side and in 10 out of 29 cases (34%) on the left side. Of 32 autopsy cases, all but one had venous valves at the venous angle. Angiography of the right brachiocephalic vein revealed internal jugular vein valves in only 15 of 38 patients (39%), and in 34 of the 38 patients (89%) some regurgitation of the valve was demonstrated. In 4 patients (11%), no regurgitation was observed. These results show that internal jugular vein valves can restrict the flow of CRCP in some cases and this may be one possible cause of the lack of correlation between perfusion pressure and flow rate.