Herein a case of cutaneous thermal injury in the leg of a patient who underwent endovenous laser (EVL) ablation of an incompetent great saphenous vein (GSV) is reported. Follow-up ultrasonography (US) of the site of skin burn showed that the burn was directly over thrombosed superficial tributaries originating from the GSV, but medial to the treated GSV. At the level of skin burn, the thrombosed GSV was 22 mm deep, but the tributaries were 1 mm deep. In addition, US showed echogenic fat surrounding and conforming to the superficial thrombosed tributaries. Based on the clinical scenario and follow-up US findings, it was concluded that the cutaneous thermal injury resulted from heated blood traveling from the 22-mm-deep GSV to the superficial tributaries directly beneath the site of skin burn.