Abstract: The penetration depth of an intraluminal device, such as a transesophageal probe or a vascular catheter, is monitored by totalizing incremental advancement and withdrawal of the device over time. For a first embodiment, the devices are provided with axially spaced-apart markings along at least a portion of their lengths. The penetration depth of such intraluminal devices into a body lumen is monitored by detecting passage of the markings past a fixed location relative to the body lumen. Usually, the markings will be optically detected in a manner which permits forward and retrograde motion to be distinguished. Thus, the net totalization of the markers will correspond to the actual penetration distance in real time. In an alternate embodiment, the incremental advancement and withdrawal may be followed by use of a contact roller. In either case, the distance can be displayed by itself or in combination with a real time image, with the distance and image optionally being recorded.