Currently, ultrasound is the most widely used noninvasive means of evaluating ovarian morphology in women with suspected polycystic ovary syndrome (PCOS). Although the most commonly used diagnostic sonographic features of PCOS are follicle number and ovarian volume, there is no complete consensus regarding the best criteria for ultrasound diagnosis. Transabdominal ultrasound has been largely superseded by transvaginal scanning because of greater resolution and, in many cases, patient preference. The transabdominal route is, of course, required in adolescent girls and virginal women who decline a transvaginal scan. The different ultrasound criteria for diagnosis of PCOS are: anthral follicle count, total ovarian volume, stromal area and ovarian area, stromal echogenicity, and vascularity. The Rotterdam criteria for the diagnosis of PCOs include the presence of 12 or more follicles in each ovary measuring 2-9 mm in diameter and/or increased ovarian volume (greater than 10 ml).