The diagnosis of Endometriosis is usually be made when patches of endometrial tissue are seen. Generally, a doctor inspects the abdominal cavity through a fiber-optic viewing tube (a laparoscope) inserted into the abdominal cavity through a small Incision just below the navel. In some cases, endometriosis can't be recognized when viewed, and the diagnosis can only be made by a biopsy, usually performed during the endoscopy.

Other procedures, such as ultrasound scans, barium enemas with x-ray, computed tomography (CT), and magnetic resonance imaging (MRI), may be used to determine the extent of the disease and follow its course, but their usefulness in diagnosis is limited. Certain blood tests that detect markers for endometriosis, such as CA-125 and antibodies to endometrial tissue - may also help a doctor follow the course of endometriosis. However, because these markers may be elevated in several other diseases, they aren't useful in making the diagnosis.