Until recently it was not possible to diagnose endometriosis on ultrasound scans. With the improvements in the quality of transvaginal scanning and better understanding of the condition it is now possible to diagnose endometriosis in most women who are affected by it. Ultrasound scans are not only useful for the detection of endometriosis, but they can also assess its severity. This is helpful in deciding whether medical treatment or surgery is best suited for individual women. Detection of endometriosis involving bowel, urinary bladder and ureters is particularly useful in women undergoing surgery. Information about the presence of disease at these difficult sites improves planning of surgery, decreases the risk of complications and helps to ensure the availability of bowel surgeons or urologists.