Endoluminal ablation either by laser or radiofrequency energy of the great saphenous vein has become the standard therapy for varicose veins caused by great saphenous vein insufficiency. The rapid recovery time and low complication profile are both reasons practitioners and patients choose this treatment modality. Complications are rare and are usually minor. This report presents a patient who presented with aneurysmal dilatation of the saphenous vein remnant, with evidence of an arteriovenous fistula, 15 months after endovenous laser therapy. The abnormality was surgically resected and the fistula successfully ligated. This may be the first report of the formation and treatment of a venous aneurysm with arteriovenous fistula involving the great saphenous vein stump after endovenous laser therapy.