Objective This study evaluates the effect of transverse and longitudinal ultrasound transducer orientation on saphenous vein cannulation during endovenous ablation. Methods A single-blinded, multicentre, randomised controlled trial was performed in patients undergoing ultrasound-guided venous cannulation for saphenous ablation. The primary outcomes were overall cannulation success and time to successful cannulation. Results In total, 100 patients were assigned to parallel longitudinal orientation and transverse orientation groups. Cannulation success was 100%. There was no significant variation in time to cannulation detected between the transverse orientation and longitudinal orientation (85 s vs. 71 s,p = 0.314). Longitudinal orientation was associated with significantly fewer needle passes [median 3 (interquartile range 1-5) vs. 2 (interquartile range 1-3),p = 0.026] and less pain (median visual analogue scale score 1 vs. 2.5,p = 0.039) than those in the transverse orientation group. Conclusion This trial has shown that while longitudinal orientation is associated with less procedural pain it has no significant effect on time to target vein cannulation during endovenous ablation.