The aim of this study was to investigate the ultrasonographic venous anatomy at the popliteal fossa in relation to tibial nerve course in normal and varicose limbs in order to detect anatomical abnormalities suggesting the potential risk of tibial nerve damage during surgery. Ninety-seven consecutive patients (194 limbs) were investigated by duplex ultrasound examination of the popliteal fossa. Forty-seven patients (48%) were candidates for surgery due to small saphenous vein (SSV) reflux. The tibial nerve course and its relation to the SSV were investigated in healthy and diseased patients. The tibial nerve ran along the medial edge of the SSV in 171 (88%) of the examined limbs. It ran behind the vein in 7 limbs (4%) and laterally in 16 limbs (8%). In this particular anatomical arrangement the SSV ends in the popliteal vein, running horizontally behind or wrapped around the tibial nerve for a distance of several centimetres. The median distance of the tibial nerve from the SSV was 0.2 cm (range: 0.1-0.3) in healthy limbs and 0.1 cm (range: 0.1-0.2) in varicose limbs, progressively diminishing as it proceeds upward. A posterior and lateral course of the tibial nerve (12%) would expose the nerve to potential damage during surgical procedures. Patient eligibility for treatment for SSV incompetence should always be based on a detailed ultrasonographic assessment of the course of the tibial nerve at the popliteal fossa in order to avoid the slightly higher risk of nerve damage due to particular anatomical abnormalities.