OBJECTIVE The aim of this study was to analyse venous diameter changes and venous reflux parameters, assessed during a standardised Valsalva manoeuvre in healthy subjects and in patients with varicose veins. METHODS Measurements were carried out in 444 vein segments, (96 legs of 48 healthy volunteers, 52 legs of 35 patients with varicose veins). The common femoral vein (CVF), the femoral vein (FV) and the great saphenous vein (GSV) were investigated. The parameters of reflux and the relative venous diameter change (VD diff %) were measured simultaneously during a standardised Valsalva manoeuvre. RESULTS Venous diameter changes during Valsalva manoeuvre (VD diff) were significantly greater in the GSV and in the deep veins of varicose patients compared to healthy subjects. The median (Interquartile range) of VD max in the CFV was: 13.1 (3.5) mm and 11.2 (3.4) mm (p=0.0002, Mann-Whitney - U test), in the FV 7.8 (2.7) mm and 6.9 (2.0) mm (p=0.01, Mann-Whitney), in the GSV: 7.3 (3.7) mm and 4.2 (1.1) mm (p<0.0001, Mann-Whitney) for the varicose and healthy veins respectively. Good correlation was seen for the retrograde peak reflux velocity (PRV) and VD diff % in varicose veins (r=0.71 (0.57 - 0.81) p<0.0001, Mann-Whitney). CONCLUSIONS Relative venous diameter--changes during a standardised Valsalva manoeuvre are significantly larger in the deep and superficial veins of varicose vein patients compared with healthy veins, the increased distensibility correlates with venous reflux parameters in varicose vein patients.