Anatomic variations of the radial artery and their effect on the use of the radial artery as a route for transradial coronary intervention (TRI) were studied. Ultrasonography of the radial artery was performed prospectively in 115 patients selected to undergo elective TRI. Anatomic variations were observed in 11 of 115 patients (9.6%). Variations included six tortuous configurations (5. 2%), two stenoses (1.7%), two hypoplasias (1.7%), and one radioulnar loop (0.9%). The hypoplastic radial arteries and the radioulnar loop were inaccessible for catheterization, and coronary intervention was planned via the femoral artery. The transradial approach was attempted in the remaining 112 patients (97.4%) with only one instance of access failure, in a patient who had a stenotic vessel. These findings indicate that anatomic variations of the radial artery is not rare, and that preoperative ultrasound examination may help to exclude patients with inaccessible arteries and those at high risk for access failure.