The relates to the guidance, positioning and placement confirmation oaf intravascular devices, as catheters, stylets, and other flexible elongate bodies that are insetted into the venk>us or arterial vasculature. Currently these goals arc achieved using x-ray imaging and in some cases ultrasound imaging. This invention provides a method to substantially mince the need for imaging rotated to placing an intravascular catheter or other device. Reduced imagine needs also reduce the amount of radiation that patients are subjected to, reduce the time required for the procedure, and decrease the cost of the procedure by reducing the time needed in the radiology department. An aspect of the invention includes, for example, an endovenous access and guidance system. The system comprises: an elongate flexible member adapted and configured to access the venous vasculature of a patient; a sensor disposed at a distal end of the elongate flexible member and configured to provide in vivo non-image based ultrasound information of the venous vasculature of the patient; a processor configured to receive and process in vivo non-image based ultrasound information of the venous vasculature of the patient provided by the sensor and to provide position information regarding the position of the distal end of the elongate flexible member within the venous vasculature of the patient; and an output device adapted to output the position information from the processor.