Ultrasound is the initial imaging modality for the assessment of endometriosis. Ovarian endometrioma, bladder endometriosis, and scar endometriosis are diagnosed reliably using ultrasound. The presence of hyperechoic wall foci and low-level echoes are very specific for endometriomas. Bilateral and multiple lesions may favor the diagnosis of endometriosis. Diagnosing deep endometriosis and adhesions is difficult with ultrasound, and laparoscopy is performed for diagnosis and staging. Endometriosis should be considered in the differential diagnosis of any woman of reproductive age who has pelvic pain or infertility.