Before the 1970s, the circuits used in electrosurgery units (ESUs) were referenced to ground. As a result, patients who came in contact with alternate paths to ground sometimes received burns. Examples of such alternate paths include current flow through metallic operating table frames, metallic frames under the instrument tables, intravenous poles, electrocardiogram probes, and towel clips. After isolation transformers were introduced in the 1970s, the ESU circuits became floating, with no direct path to ground. This significantly reduced the incidence of burns due to electrosurgery. This article evaluates the potential for alternate return site burns when using modern ESUs. A computer simulation and a laboratory test with a real ESU were performed. It is concluded that under specific circumstances a patient can be burned after 20 seconds of continuous ESU activation. These circumstances include (1) activation of the ESU without contact between the active electrode and the patient, (2) a small alternate return site contact area of 1 cm2, and (3) the use of a high-power, 200-W cut mode.