In medicine, the ileal pouch–anal anastomosis (IPAA), also known as restorative proctocolectomy (RPC), ileal-anal reservoir (IAR), an ileo-anal pouch, ileal-anal pullthrough, or sometimes referred to as a J-pouch, S-pouch, W-pouch, or a pelvic pouch, is an anastomosis of a reservoir pouch made from ileum (small intestine) to the anus, bypassing the former site of the colon in cases where the colon and rectum have been removed. The pouch retains and restores functionality of the anus, with stools passed under voluntary control of the person, preventing fecal incontinence and serving as an alternative to a total proctocolectomy with ileostomy.

During a total proctocolectomy, a surgeon removes a person's diseased colon, rectum, and anus. For the ileostomy, the end of the small intestine is brought to the surface of the body through an opening in the abdominal wall for waste to be removed. People with ileostomies wear an external bag, also known as an ostomy system or stoma appliance, to collect waste which can be emptied and changed as needed.

With an optional ileo-anal pouch procedure, the pouch component is a surgically constructed internal intestinal reservoir; usually situated near where the rectum would normally be. It is formed by folding loops of small intestine (the ileum) back on themselves and stitching or stapling them together. The internal walls are then removed thus forming a reservoir often referred to as a 'pouch'. The reservoir is then stitched or stapled into anal area where the bottom of the rectum was. The first pouch anal-anastomosis surgery in the world was performed by British surgeon Sir Alan Parks in 1976 at the London Hospital (called the Royal London Hospital since 1990). After the first surgery, he continued to develop the procedure at St Mark's Hospital in London along with his colleague Professor John Nicholls.

Pouch surgery is elective, meaning it is entirely optional, and should be done on the basis of choice by people who doctors deem suitable for a pouch after medical evaluations. Pouch surgery is considered reconstructive with the benefit being for quality of life and not disease removal, similar in theory to a breast reconstruction after a mastectomy removes diseased breast tissue. Before a pouch is created, a person's diseased colon and rectum are removed. After disease removal, standard medical screening exams for pouch candidates include but are not limited to biopsies, radiology imaging, sphincter function tests, fertility consultations for people of childbearing age with the wish to get pregnant, and psychological support due to intensity of the pouch operations.

A similar ileal pouch without the anal anastomosis is a Kock pouch. A Kock pouch is also called a 'continent ileostomy' because while a person has a pouch constructed inside their body, it is located near the abdominal wall and empties via a stoma from the ileum at the person's convenience. A Kock pouch does not restore the anal function. The procedure was first premiered by Finnish surgeon Dr. Nils Koch in Sweden during 1969. It was an evolution in bowel surgery because it created an ileum pouch for storage of waste inside the body eliminating the need for an external bag for waste collection. An ileostomy without a Koch pouch functions constantly, meaning, a patient with ileostomy by itself is incontinent because waste is always moving down the bowel and thus the need for an external appliance bag. Koch pouch surgery is also elective surgery that only provides a reconstructive benefit after disease removal. It should be the patient's optional choice based on how a person wants to live their life.