Valvular incompetence in the great saphenous vein (GSV) is the most common cause of superficial venous insufficiency and symptomatic varicose vein development. Recently, less invasive modalities such as foam sclerotherapy, radiofrequency ablation (RFA), and endovenous laser treatment (EVLT) have gained popularity in the treatment of saphenofemoral junction and saphenous truncal incompetence over the traditional approach of surgical ligation and stripping. Here, we present the case of a 32-year-old woman who underwent EVLT and was diagnosed subsequently with ipsilateral external iliac arteriovenous (AV) fistula and high-output cardiac failure. She was stabilized medically and treated surgically with a covered stent placed in the external iliac artery with complete resolution of the fistula and cardiac failure. We reviewed the literature and discuss the complications of AV fistulae after EVLT.