Size matching of radial artery conduits to coronary arteries is important as it affects the long-term patency. However, factors affecting radial artery size have not been adequately investigated. We retrospectively reviewed 327 consecutive patients who had duplex ultrasonography of their radial arteries over a 2-year period. There were 225 men and 102 women. The mean radial artery size was 2.45 +/- 0.54 mm. The factors found to positively affect the size of the radial artery were sex, hypertension, and hyperlipidemia. Diabetes mellitus and age were found to negatively affect radial artery size. Renal disease, race, and smoking did not significantly influence the size of the radial artery. However, as the R squared of this model was insignificant, further studies need to be undertaken to determine other factors that may influence radial artery size.