Abstract: A drainage device, in particular a catheter, provided with an inflatable balloon adjacent one end which is designed to be inserted into a vessel which is to be drained. This insertion end comprises two branches which are interconnected at their free ends by the inflatable balloon and which are arranged, in the uninflated state of the balloon, to extend substantially parallel to the longitudinal axis of the device and to constitute substantially no increase in the width or diameter of the device. In the inflated state of the balloon, at least one of the said branches diverges from the longitudinal axis of the device to permit access to a drainage tube extending through the device.