The endoscopy of blood vessels represents an important intra-operative diagnostic procedure in vascular surgery. This is especially true in controlling semiclosed desobliteration of the aorto-iliac andfemoro-popliteal segment, furthermore, in examining the complete removal of thrombi in acute phlebothrombosis. Technically a working instrumentarium, a passable vessel calibre and a translucent milieu are necessary (temporary clamping of the bloodstream by clamps or balloon catheter, continuous perfusion through the endoscope). The advantage of an examination on an open vessel by a relatively simple method compared with the conventional intra-operative procedures is quite obvious. The endoscopy of major veins will bring new thought about the mechanism of venous valves and will lead to a fast and certain diagnosis of the so-called pelvic vein calcar.