More than 40,000 patients undergo treatment for superficial venous incompetence (varicose veins) in the UK each year. Previously the majority underwent conventional surgery with its associated inconvenience and morbidity. Endovenous laser ablation (EVLA) is a relatively new minimally invasive technique that abolishes superficial venous reflux and is an alternative treatment for some patients. Although early studies have shown it to be safe and effective for great saphenous vein (GSV) reflux there remain many questions relating to optimizing the technique and the range of patients for whom it is suitable. This thesis evaluates factors that may influence EVLA efficacy for GSV reflux and other sites of deep to superficial venous incompetence (small saphenous, anterior accessory GSV, paradoxical reflux). It also assesses changes in venous haemodynamics after EVLA which has led to recommendations on improving treatment outcomes. Further, a prospective database of patients undergoing EVLA and conventional surgery has been maintained (clinical and duplex ultrasound follow-up at 6, 12 & 52 weeks, quality of life data) which has provided additional evidence on the management of patients with varicose veins. Briefly, these studies have confirmed that laser energy density (J/cm) is the crucial factor determining successful truncal vein ablation following EVLA and that appropriate patients can continue warfarin therapy without compromising the safety or efficacy of treatment. Other studies demonstrate the transition of ablated truncal veins from a non-compressible “thrombosed” vein to becoming non-visible 1 year after EVLA. Further, sapheno-femoral junction (SFJ) tributaries remain patent and competent with no adverse impact on clinical outcome whilst SFJ neo-vascularisation occurs much less often after EVLA than surgery. In patients with persistent below-knee GSV incompetence after EVLA residual symptoms are more likely and there is a greater need for sclerotherapy for residual varicosities. A RCT subsequently confirmed that extended ablation of the below-knee GSV achieved superior outcomes.