The Trendelenburg position, named for Doctor Friedrich Trendelenburg, is a patient position which is used for certain kinds of medical procedures. When a patient is placed in the Trendelenburg position, she or she is placed in a supine position, meaning that the patient is lying face up, and the table on which the patient lies is angled so that the feet are above the head. In the reverse Trendelenburg position, the patient's orientation is switched so that the head lies above the feet.

This patient position was originally developed for use in surgery and it is still seen used in this way. For gynecological and abdominal surgeries, tilting the head downwards can pull the intestines out of the pelvis, creating a clearer surgical field which is easier to see and work in. This position is also sometimes used when a physician is attempting to turn a baby before birth, as reversing the usual pull of gravity creates more room to rotate the baby so that she or he will not be in a breech position.

Historically, the Trendelenburg position was recommended as a position which could be used for people recovering from shock, people who need increased cerebral perfusion, people in anaphylaxis, and divers in recovery from deep dives. However, the medical literature now suggests that this is actually not wise. Patients in this position are at increased risk of airway problems and may aspirate vomit and other fluids as a result of being placed in this position. For this reason, many practitioners no longer routinely use the Trendelenburg position on patients in these situations.

Another case in which this patient position may be used is during labor. If there are concerns about the umbilical cord being pressured and cutting off the supply of oxygen to the baby, lying in this position can relieve the pressure and may also provide working room for the delivery attendant to move the cord to reduce the risks of delivery. Some women may also find that lying in this position helps with the cramps associated with menstruation.

More infamously, this position is utilized in the torture tactic known as “waterboarding.” Because the patient's airway can already be subject to obstruction in this position, the sense of simulated drowning is heightened when someone in a Trendelenburg position is subjected to waterboarding. It can also be easier to control subjects when they are strapped to a table in an upside down position.