Endometriosis is a common clinical condition where functional endometrial tissue is found outside the uterine cavity. Although most of this ectopic tissue tends to occur within the pelvis, on rare occasions, they can also be found in unusual locations, such as the thoracic cavity, perianal, episiotomy scar, and previous abdominal wound sites. This is a case report of a healthy 41-year-old Chinese female who presented with a painful perianal lump which was subsequently investigated and excised. The diagnosis of perianal endometriosis was made upon histological examination of the tissue. Many theories attempt to explain the phenomenon of endometriosis in the perianal region. In this case, the implantation theory is the likely explanation as the patient had a significant history of 3 normal vaginal deliveries which were followed by episiotomies. Advancements in endo-anal ultrasound (EAUS) have aided in the planning of surgery for this lesion.
