Abstract Background: Great saphenous vein incompetence is in-volved in the majority of cases of varicose disease. Standard pre-interventional assessment is required to decide the treat-ment modalities. GSV diameter measured at sapheno-femoral junction, proximal thigh, distal thigh, knee, proximal leg, distal leg. Analysis done to find at which diameter size the reflux expected to occur. Aim of Study: To investigate a possible correlation of GSV diameters measured at sapheno-femoral junction, prox-imal thigh, distal thigh, below knee and at mid leg and there relation to the reflux. Patient and Methods: Study involved 100 limbs from outpatient vascular clinic, GSV diameter measurement at the sapheno-femoral junction, at the proximal thigh, at the distal thigh, below the knee, mid leg in correlation to reflux. Results: SFJ reflux (group I) at 7.16±2.30mm, proximal thigh (group II) at 6.60±1.89mm, distal thigh (group IIIa) at 6.12±1.63mm, knee (group IIIb) at 5.78±1.60mm, proximal leg (group IV) at 4.6±1.24mm, and mid leg (group V) at 3.59±  1.16mm. Conclusions: Measurement at six sites revealed higher sensitivity and specificity to predict reflux, GSV diameter correlates with reflux.