Objective: Remaining symptoms after treatment of superficial venous incompetence is a common problem. Duplex ultrasound is often used during follow-up, but does not permit an overall quantification of venous function. We have developed a plethysmographic method using occlusion cuffs for separation of superficial and deep venous reflux. By assessing the superficial component it is possible to quantify a potential suboptimal hemodynamic treatment in patients with superficial venous incompetence. The aim was to examine whether patients with hemodynamically quantifiable remaining reflux after treatment experience impaired clinical outcomes.Methods: This single-center prospective cohort study evaluated 156 limbs with great saphenous vein incompetence treated with radiofrequency ablation or high ligation and stripping. Duplex ultrasound and strain-gauge plethysmog-raphy (SGP) with and without selective superficial occlusion were performed before and one-year after treatment. Time taken (seconds) to reach 50% of the venous volume (T-50) was evaluated. A difference in the T(50 )of >5 seconds between postoperative strain-gauge plethysmography with and without superficial occlusion was defined as remaining reflux. The Venous Clinical Severity Score (VCSS) and Aberdeen Varicose Vein Questionnaire (AVVQ) were evaluated and compared between patients with and without remaining reflux. Multivariable logistic regression was used to evaluate risk factors for remaining plethysmographic reflux.Results: In all patients, median (25th, 75th percentile) T-50 increased preoperatively from 7 seconds (3, 12 seconds) to 17 seconds (11, 28 seconds) (P < .001)1 year after treatment. The VCSS and AVVQ were reduced (VCSS, 8.0 [6.0, 10.0] vs 3.0 [1.0, 5.0] [P < .001]; AVVQ, 21.8 [15.8, 32.1] vs 6.4 [2.2, 11.0] [P < .001]). Of the 156 limbs, 87 (56%) demonstrated remaining reflux 1 year after treatment. Patients with remaining plethysmographic reflux displayed higher median (25th, 75th percentile) VCSS (3.0 [2.0, 5.0] vs 2.0 [1.0, 4.0]; P= .012) and AVVQ (7.5 [2.7, 14.9] vs 4.7 [1.6, 9.2]; P= .025). Multivariate logistic regression showed that higher preoperative C in the Clinical Etiology Anatomy Pathophysiology classification (CEAP) (odds ratio [OR], 2.9 [95% confidence interval [CI], 1.34-6.46), age (OR, 1.03; 95% CI, 1.001-1.065), small saphenous vein incompetence (OR, 4.2; 95% CI, 1.30-13.73) and postoperative great saphenous vein reflux below the treated area (OR, 2.16; 95% CI, 1.02-4.56) were significant risk factors for remaining plethysmographic reflux.Conclusions: A majority of treated limbs showed quantifiable reflux 1 year after intervention and these patients displayed worse patient related outcomes assessed with the VCSS and AVVQ. Remaining plethysmographic reflux was associated with preoperative small saphenous vein incompetence and reflux below the treated area as well as advanced age and higher C in CEAP.