Duplex ultrasound is widely used for studying the venous system of the lower extremities in practical medicine. Despite the apparent simplicity, it is considered a rather complex and «operator-dependent» tool, mainly due to the variability of the anatomy of venous system. The study usually starts at the upper thigh, where the superficial and deep veins are identified. The initial reference point is the safeno-femoral junction. Normal anatomy characterizes the femoral vein as single trunk, but in practice there may be more of them. This makes diagnostics to be rather difficult. The article presents two clinical observations of rare topographical variants of femoral vein, that has to be taken into account during ultrasound examination and while performing venous intervention.