OBJECTIVES To evaluate the safety and effectiveness of endovenous cyanoacrylate-based embolization of incompetent great saphenous veins. METHODS Incompetent great saphenous veins in 38 patients were embolized by cyanoacrylate bolus injections under ultrasound guidance without the use of perivenous tumescent anesthesia or graduated compression stockings. Follow-up was performed over a period of 24 months. RESULT Of 38 enrolled patients, 36 were available at 12 months and 24 were available at 24 months follow-up. Complete occlusion of the treated great saphenous vein was confirmed by duplex ultrasound in all patients except for one complete and two partial recanalizations observed at, 1, 3 and 6 months of follow-up, respectively. Kaplan-Meier analysis yielded an occlusion rate of 92.0% (95% CI 0.836-1.0) at 24 months follow-up. Venous Clinical Severity Score improved in all patients from a mean of 6.1 ± 2.7 at baseline to 1.3 ± 1.1, 1.5 ± 1.4 and 2.7 ± 2.5 at 6, 12 and 24 months, respectively (p < .0001). Edema improved in 89% of legs (n = 34) at 48 hours follow-up. At baseline, only 13% were free from pain. At 6, 12 and 24 months, 84%, 78% and 64% were free from leg pain, respectively. CONCLUSIONS The first human use of endovenous cyanoacrylate for closure of insufficient great saphenous veins proved to be feasible, safe and effective. Clinical efficacy was maintained over a period of 24 months.