Abstract: A multi-lumen catheter is formed by first introducing one end of an expandable tube into the blood vessel. A divider is then inserted into the distal end of the tube and extends the length of the tube, thereby dividing the tube into a plurality of the separate lumens. Insertion of the divider causes radial expansion of the tube which substantially seals the opening in the wall of the vessel. In one embodiment, the divider has a hollow triangular cross-section which creates four separate lumens. A series of raised protrusions extending outwardly from the sides of the divider prevent collapse of the tube against the divider.