Transvaginal ultrasonography has become the primary test in the diagnosis of pelvic endometriosis and adenomyosis. A review of the literature on the diagnostic accuracy of ultrasonography in pelvic endometriosis and adenomyosis, as well as a comparison with magnetic resonance imaging, will be presented. Criteria for diagnosis of an endometrioma according to robust prospective data together with guidelines as to adequate reporting of the location of deep infiltrating endometriosis will be given. The sonographic features of adenomyosis including the differential diagnosis between focal adenomyosis and a uterine fibroid are reviewed. The available data in the literature on ultrasound diagnosis of pelvic endometriosis and adenomyosis, their clinical relevance, and their limitations are discussed.