Internal rectal prolapse (IRP) is medical condition involving a telescopic, funnel-shaped infolding of the wall of the rectum that occurs during defecation. The term IRP is used when the prolapsed section of rectal wall remains inside the body and is not visible outside the body. IRP is a type of rectal prolapse. The other main types of rectal prolapse are external rectal prolapse (where the prolapsed segment of rectum protrudes through the anus and is visible externally) and rectal mucosal prolapse (where only the mucosal layer of the wall of the rectum prolapses).

IRP may not cause any symptoms, or may cause obstructed defecation syndrome (difficulty during defecation) and/or fecal incontinence. The causes are not clear. IRP may be the first stage of a progressive condition that eventually results in external rectal prolapse. However, it is uncommon for IRP to progress to external rectal prolapse. It is possible that chronic straining during defecation (dyssynergic defecation / anismus), connective tissue disorders, and anatomic factors (e.g. loose connection of rectum to the sacrum, redundant sigmoid, deep pouch of Douglas) are involved. If IRP is causing symptoms, treatment is by various non-surgical measures such as biofeedback, or surgery. The most common surgical treatment for IRP is ventral rectopexy.

IRP is often associated with other conditions such as rectocele, enterocele, or solitary rectal ulcer syndrome. IRP usually affects females who have given birth at least once, but it may sometimes affect females who have never given birth. About 10% of cases of IRP are in males. More severe forms of IRP are associated with older age.

Three main types of rectal prolapse are usually identified. These are external rectal prolapse (full thickness / complete rectal prolapse), internal rectal prolapse, and rectal mucosal prolapse. There are several different synonymous terms for IRP, and it has no universally accepted definition.

Internal rectal prolapse (IRP) is a telescopic, funnel-shaped invagination (infolding) of the rectal wall that occurs during defecation. The prolapsed segment of rectal wall remains confined within the rectum or the anal canal and is not visible externally (i.e., proximal to the anus). IRP may be a circumferential infolding (involving the full circumference of the rectal wall) or unilateral infolding (involving only one side of the circumference).

Usually IRP is defined as a full thickness prolapse of the rectal wall (i.e., involving all three layers). However, sometimes IRP is defined as involving the full thickness of the rectal wall or only part of it.

Many synonyms for IRP include the term intussusception. When used unqualified, the term intussusception (or intestinal intussusception) refers to telescopic infolding of a section of the wall of the intestine into the portion directly in front. This is sometimes conceptualized as pulling a sock partially inside out, creating a tube within a tube. The part that moves into the other is called the intussusceptum, and the part that receives it is called the intussuscipiens. This condition usually occurs in the small intestine in children. It less commonly happens in the colon or in adults. Terms like rectal intussusception, rectoanal intussusception, internal intussusception refer to IRP, which is an entirely different medical condition from intussusception (intestinal intussusception).

External rectal prolapse (also termed complete / full-thickness rectal prolapse, or procidentia) is when the prolapsed segment of rectal wall protrudes through the anus. External rectal prolapse may be visible externally while the individual is straining, whereas IRP is not visible externally and can only be detected with investigations like proctoscopy or defecography. External rectal prolapse is a full thickness, circumferential prolapse. Usually it is possible to push the prolapsed rectal wall back into the body, but sometimes it may become strangulated which may represent a medical emergency.