Obesity is a risk factor for chronic venous disease (CVD) of the lower limbs (LL), affecting venous anatomy and physiology. Weight loss after bariatric surgery (BS) can reduce intra-abdominal pressure, improve mobility, and ultimately improve venous hemodynamics and CVD-related symptoms. There are no studies in the literature that adequately assess the effect of the obesity and BS on the LL veins, especially the saphenous veins (SV). The aim of this study was to evaluate the effects of obesity and BS on the saphenous veins. This is a longitudinal prospective study carried out from 2019 to 2021 with 19 patients, totaling 38 LL, underwent clinical evaluation (CEAP Classification) and by Doppler ultrasonography, to analyze their SV diameter and reflux measurements, in the preoperative period and again 6 months to 2 years after BS being performed. There was no statistical difference between the groups regarding the characteristics of reflux in the SV among the evaluated LL. There was no significant increase in the diameter of the great SV in the majority of its segments. The groups were similar in terms of the small SV diameters. Moreover, a significant reduction in the clinical class of CEAP was observed after BS. Obesity and bariatric surgery had no influence on diameter or reflux in saphenous veins, but a reduction in the CEAP Clinical Classification was observed in the postoperative period.