The purpose of this study was to evaluate and quantify the effects of Ultra-Low Frequency Transcutaneous Electrical Nerve Stimulation (ULF-TENS) on the Central Nervous System, using electroencephalography. The research was conducted on a study group of twelve patients, and a control group of six. Patients were chosen between the ages of twenty and thirty years old, and all had occlusal flags without pain. The electroencephalography patterns were registered, for each patient in the study group, before and after the application of 60' of the ULF-TENS. In nine of the twelve cases studied, a diminution of the cerebral rhythm was registered along with the appearance of a sedative effect caused by an increment in Alfa waves and a state of hypo-alertness caused by an increment in the theta rhythm. An identical effect was registered in one subject of the control group while another subject had an increased cerebral rhythm, and in the remaining four subjects, all values remained invariable. The study demonstrated two important points. First, it confirmed the utility of the EEG as a noninvasive useful method in order to study the central effects of the ULF-TENS, and second, also positive, it revealed the sedative effects on the central nervous system registered by the EEG.