The anatomy of the venous system in the pedicles of the radial forearm and anterior tibial reverse flow flaps was investigated in fresh cadavers (n = 6) and their drainage pathways were observed in a radiographic perfusion study of the veins of 2 radial forearm and 2 anterior tibial pedicles. The venous system was found to consist mainly of three types of veins: venae comitantes, communicating veins between the venae comitantes, and vasa vasorum. Valves were identified in all three types of vein. In the venous system, including the vasa vasorum, there was no route of reverse flow that did not pass directly through valves. Valve incompetence was demonstrated in the radiographic perfusion study. However, valve incompetence did not occur in all valves and a difference in valve resistance against reverse flow pressure existed. Veins with relatively weak valve resistance became the drainage pathway. A possible cause of the difference in valve resistance was differences in the anatomy of the valve sinuses.