Endometriosis is defined as the presence of endometrial-like tissue outside the uterus. Deposits are commonly distributed on the ovaries, uterosacral ligaments, pouch of Douglas, rectum and sigmoid colon, bladder and ureter. Endometriosis is common, affecting 10% of the female adult population and up to 50% of women with infertility. Risk factors include early menarche, late menopause, delayed childbearing, vaginal outflow obstruction and a first-degree relative affected. Women commonly present to their GP with pelvic pain, painful intercourse or subfertility. Classically the pain starts several days before the period which is extremely painful. After the period, symptoms tend to improve until mid-cycle when the pattern repeats again. Patients also complain of fatigue. Abdominal palpation, bimanual and speculum examination are important to identify signs of endometriosis, but also to exclude alternative diagnoses such as fibroid uterus, infection or pregnancy. However, a normal examination does not exclude a diagnosis of endometriosis. Serum CA125 can be raised in endometriosis but is not specific or sensitive for the condition and is therefore not recommended as a screening test. A normal pelvic ultrasound scan does not exclude a diagnosis of endometriosis. The gold standard investigation for endometriosis is laparoscopy and biopsy with histological confirmation. Referral should be considered if pain is not controlled with simple analgesia or the diagnosis is suspected in a woman who is actively trying to conceive. Early referral should be considered in women with abnormal examination findings, or an abnormal ultrasound result.