Background: The correct positioning of the laser tip at the saphenofemoral or saphenopopliteal junction during endovenous laser therapy is paramount to ensure a safe and effective procedure. The aim of this study was to demonstrate how patient positioning and tumescence infiltration can affect this safe junctional distance. Methods: A retrospective review of a prospectively maintained database was carried out for all patients who received endovenous laser treatment for symptomatic varicose veins between February 2008 and February 2014 in one surgeon's practice in a teaching hospital vascular unit. The junctional distance of the laser tip from the saphenofemoral or saphenopopliteal junction was measured two times during the procedure: before tumescence and before laser deployment with the patient in a Trendelenburg position. Results: Junctional distance was found to have increased in 62% cases (490 patients; great saphenous vein [GSV]. 348; small saphenous vein [SSV],142). Of these, 17% (84) required the laser tip to be advanced (GSV. 56: SSV. 28) to maintain a desired junctional distance of 0.75 to 2 cm. In 185 patients (23%), the junctional distance was noted to have been reduced (GSV,155; SSV, 30), with 58% (GSV, 79; SSV, 28) requiring the laser tip to be withdrawn to the desired junctional distance; 23% of patients (185) had no change in the junctional distance. Conclusions: This study has demonstrated the effect of tumescence infiltration and Trendelenburg positioning on laser tip placement, and thus a final junctional measurement before activation of the laser is recommended to maintain a safe and optimal junctional distance.