Objectives Few studies compared both ultrasound and histological approaches for the same series of patients with chronic venous disease (CVD). We aimed to assess the diagnostic performances of duplex ultrasound assessment (US) of Vein Wall Thickness (VWT) among patients with CVD. Methods 38 adults with primary varicose veins having undergone Great Saphenous Vein thermal ablation with phlebectomy, and agreeing to biopsy of the Posterior Accessory Great Saphenous Vein (PASV) were consecutively included in a two-center prospective study. VWT assessment of the PASV was performed using both US, and microscope examination. High values for microscope-assessed VWT were defined at > 0.5 mm. Results The mean age was 53.0 ± 13.1 years, 71% were women. Maximization of US performances was obtained with a threshold of 0.6 mm: Sensitivity (Se) = 92.9%, Specificity (Sp) = 91.7%, positive (86.7%) and negative predictive value (NPV) (95.7%), positive (11.1) and negative likelihood ratio (NLR) (0.07). Conclusions US assessment of VWT could be a non-invasive tool for diagnosis and follow-up in CVD, and an interesting in vivo parameter complementing diameter and reflux measures, with a view to optimizing treatment. It could help to determine i) the energy level necessary in case of endovenous laser ablation, and ii) the sclerosing agent concentration in case of chemical ablation.