While endovenous thermal ablation (ETA) become first choice of treatment for varicose veins, overuse of ETA for the inappropriate indication is growing problem. ETA is performed not only on varicose cases without symptom but also non diseased cases with segmental reflux of saphenous veins or no reflux. Indications of ETA was demonstrated in "the Clinical Practice Guidelines for ETA for Varicose Veins 2019" by Japanese Society of Phlebology. Purpose of this supplement is description of basics of correct indication for ETA. We also demonstrate the typical case of overuse of ETA for wrong indication. (This is a translation of Jpn J Phlebol 2020; 31: 39-43.).