Cannulation of the arterial system is an invasive monitoring technique that readily is justified by its high information yield and minimal discomfort and risk to the patient and is commonly performed in the ICU and operating room, allowing continuous monitoring and graphic display of the systemic arterial blood pressure, and repeated analysis of arterial blood gases. The major complications subsequent to cannulation are thrombosis and occlusion pain at the puncture site, hematoms and infection. We performed a clinical study on complications following percutaneous arterial cannulation in 378 patients with radial artery cannulation and 172 patients with dorsalis pedis artery cannulation who had undergone surgery at Kyung Hee University Hospital from April to September, 1987. The patients were examined to confirm the patency of the collateral circulation of the hand and foot before cannulation and the frequency of complication was studied by physical examination and the Doppier technique on the 1st, 7th and 10th days after decannulation. The results were as follows: 1) The most common complication of radial artery cannulation was ecchymosis(41.8%) and the next common complications were abnormal blood flow(17.5%), abnormal pulse (13.2%), sensory change(1.3%) and infection(0.3%). 2) The most common complication of dorsalis pedis artery cannulation was ecchymosis(34.9%) and the next common complications were abnormal blood flow(19.8%), abnormal pulse(12.8%), sensory chang(1.7%) and infection(0.6%). 3) The crrelation of sex, duration of cannulation, number of punctures and age to the incidence of abnormal flow was studied in both arteries. Abnormal flow was only significantly related to females(p<0.05) in both arteries. 4) The correlation of both arteries to the incidence of abnormal flow under several circumstances was studied. But neither artery did not revealed a significant difference to the incidence of abnormal flow. 5) No permanent ischemic damage to the hand or foot occurred in any patient in this study. Therefore, we concluded that radial artery cannulation is a low-risk highly beneficial monitoring technique and careful dorsalis pedis artery cannulation provides a relatively safe, reliable and available to the radial artery with caution.