The perineal nerve is a branch of the pudendal nerve and serves the external genitalia of both sexes as well as the perineal area, which is the space between the scrotum and the anus in men, and between the vagina and the anus in women. Identified as the largest branch of the pudendal nerve, the perineal nerve itself also has two branches, the superficial perineal nerve and the deep perineal nerve, which themselves branch out into smaller nerves. Superficial perineal nerves branch out into smaller nerves that serve the scrotum in men and the labia in women. Deep perineal nerves, also known as the muscular perineal nerve, connect to the urethra and, in men, branch out into nerves in the penis. They also branch into various areas of the perineum and serve muscles that are directly responsible for ejaculation in men and orgasm sensation in both men and women.

Under certain circumstances, perineal nerve damage can occur, leading to various unpleasant symptoms. Some causes of perineal nerve damage include damage caused during childbirth or during surgical procedures such as a vasectomy, or, more rarely, damage from the seat of a bicycle after extensive time riding. An episiotomy, in which a cut is made in the perineum to enlarge the birth canal, can lead to perineal nerve injury as well as other problems in the perineal area, including damage to the anal sphincter. In many cases, the perineum tears during childbirth, which can also lead to damage to the perineal nerve. One function of this important nerve is to contract the sphincter that controls the opening and closing of the urethra, so one of these symptoms can be stress incontinence, and damage to the nerve also can lead to decreased sexual sensation and difficult orgasm in both sexes.

Less common is entrapment of the perineal nerve or of the pudendal nerve, in which constant pressure is exerted on the nerve by inflammation, a tumor or other abnormal swelling in adjacent ligaments or other tissues in the area. This can lead either to constant pain or to numbness in the perineum, anus, scrotum or labia. Treatment includes self-care, anti-inflammatory medication and rest if the entrapment is caused by inflammation. Serious cases that do not respond to minimal, non-invasive treatment after a period of about six weeks can require a series of injections or even surgical correction of the nerve entrapment.