The Access guide catheter provides passage for therapeutic and diagnostic devices through vessels or conduits that return substantially in a direction from which they originated. One application is for delivery of therapeutic catheters to the carotid or cerebral arteries via access from the radial or brachial artery. The guide catheter enters the aorta from one of the great vessels, forms a closed loop in the aorta, and is directed back into a great vessel in an opposed direction. The distal portion of the guide catheter is advanced into the great vessel for support. Further support is attained by providing tension to the proximal shaft of the guide catheter. Flexibility of the guide catheter allows diagnostic angiograms to be performed prior to delivery of a therapeutic catheter or device.