Percutaneous radial artery cannulation has become a common technique for continuous monitoring of arterial blood pressure and serial sampling fo arterial blood in critically ill patients and hypotensive anesthesia. Although the method is generally safe and simple it frequently results in temporary radial artery occlusion, which is usually asymptomatic and resolves spontaneously. But occationally which the ulnar arterial collateral circulation is poor, occlusion of the radial artery can cause ischemia or even frank gangrene of the hand. The influence of cannula size or shape, duration of cannulation, frequency of puncture trial and patient's age on the incidence of vessel occlusion remains controversial. We evaluated radial arterial function utilizeing physical examination and Doppler flow measurement in fourty-seven patients following percutaneous cannulation. Arterial occlusion occured in 12.8% and hematoma in 31.9% of fourty-seven patients. The incidences of occlusion and hematoma were more frequent when the attempted puncture was more than three times and the duraion of cannulation was more than six hours. Hematoma disappeared spontaneously several days after and collateral circulation was good without other vascular complication in all six patients who had arteiral occlusion.