Objectives: Primarily, to determine the association between the clinical severity of primary varicose veins and different reflux patterns in an anatomic and haemodynamic clinical study using duplex ultrasonography (DU). Secondly, to analyse the association of clinical severity with other aspects, such as risk factors for chronic venous insufficiency (CVI) and other concurrent diseases. Method: A total of 2036 limbs were evaluated using DU. Clinical status was characterized by the CEAP (clinical, aetiological, anatomical and pathological elements) classification. The degree of clinical severity was grouped into two categories, mild to moderate CVI (C 1 -C 3 ) and severe CVI, characterized by the presence of skin changes (C 4 -C 6 ). We analysed the association of the different reflux patterns with CEAP status. Results: Saphenofemoral junction (SFJ) reflux of the great saphenous vein (GSV) was associated with the most severe form of the disease (odds ratio [OR] ¼ 2.96; confidence interval [CI] 95%: 2.2-3.8), whereas competent SFJ of the GSV with reflux from proximal veins (OR ¼ 2; CI 95%: 1.4 -2.7) and the pure non-saphenous reflux (OR ¼ 4.1; CI 95%: 1.8-9.0) were associated with mild to moderate CVI. Obesity increased the frequency of severe CVI 2.7 times (OR ¼ 2.7; CI 95%: 1.6-4.6); being a woman also increased the frequency of more severe disease 1.3 times (OR ¼ 1.3; CI 95%: 1.0-1.7). Conclusion: Anatomical and haemodynamic studies by DU are postulated as a useful diagnostic tool that allow, by identifying the pattern of venous reflux of varicose pathology, characterization of the probable association to CVI clinical severity.