the all internal.....ANS..meditron system with two internal leads..each lead has one tab with 5 contacts ... I am wired for both legs... I have the newer model which is the smaller unit, I had to wait until it was manufactured due to my stature my Dr. insisted on this size..less weight for me to carry around.... The area where the box lives, my left hip is always tender and my spine , to me feel like I have wires which sometimes it can be bothersome.. but manageable..Plz. let me know if I can help you answer more questions....KS