Aim. Assessment of the function of veno-venous bypass operations in postthrombotic disease with the use of ultrasound duplex scanning. Methods. The results of veno-venous bypass procedures are presented including crossover autovenous bypass for unilateral postthrombotic iliac vein obstructions (during short-term postoperative period in 56 patients, during long-term period - in 68) and saphenopopliteal bypass for femoral vein obstruction (in 12 patients). Results. Functional tests making ultrasound duplex scanning more informative in assessment of the function of bypass operations were developed. It was determined that most of crossover grafts (70.6%) have a propensity to equal «physiological» dilation leading to the requisite venous drainage from an affected extremity. Some grafts (23.6%) undergo pathological transformations like local and diffused deformed dilation, сicatricial stenosis that diminish venous drainage and require reintervention on the graft. Venous hemodynamic studies of the affected extremity with the graft being open and cross-clamped showed that in 73% of the patients the major role in the maintenance of venous return is played by crossover bypass. Long-term outcomes in 56 patients after 15 years proved patency of crossover grafts in 43 patients (79.6%). In 11 out of 12 patients (91.7%) examined during long-term postoperative period saphenopopliteal grafts were patent. It was demonstrated that they are capable of prolonged functioning without pathological dilation. Long-term outcomes of the procedure proved reliable function of the grafts and improvement of regional venous hemodynamics. Conclusion. Ultrasound duplex scanning is the optimal method of the assessment of short-term and long-term outcomes of reconstructive bypass operations due to their noninvasiveness, safety, and high resolving power and the possibility of repetitive qualitative and quantitative studies of venous system including those in community setting.