OBJECTIVES:The venous clinical severity score (VCSS) and the Aberdeen varicose vein questionnaire (AVVQ) improve after treating chronic venous insufficiency (CVI). The aim was to examine how and why they improve by evaluating the change in each individual question. METHODS:This was an analysis on prospectively collected data from a clinical study on 100 patients (58% female) with CVI (C2 = 34, C3 = 14, C4a = 29, C4b = 9, C5 = 7, C6 = 7) who were randomized to endovenous laser ablation (n = 50) or foam sclerotherapy (n = 50). The change scores (performance) of each question of the VCSS (questions 1-10) and the AVVQ (questions 1-13) were calculated by subtracting the score at three weeks, and three months, from the pre-treatment score. RESULTS:Both the median, interquartile range (IQR), VCSS and the AVVQ scores improved from 6 (4) and 21.4 (15.1) at baseline to 3 (4) and 18.6 (12.1) at three weeks (P < 0.0005, P = 0.031) to 2 (3) and 8.8 (13.6) at three months, (P < 0.0005, P < 0.0005), respectively. The performance of the first three questions of the VCSS (pain, extent of varicosities, oedema) were the most contributory to the overall score. Questions 5, 7, 8, 9 on ulceration improved the most individually but did not contribute significantly to the overall score. Questions 5, 9 of the AVVQ on stocking use and ulceration failed to contribute statistically to the overall improvement at three months. CONCLUSION:The majority of the individual questions of the VCSS and AVVQ responded to change. However, the cause of a poor response was multifactorial with statistical dilution playing a significant role. Stratification of patients according to ulceration may allow better comparisons.