In this radiology lecture, we review the ultrasound appearance of polycystic ovarian syndrome (PCOS)! Key teaching points include: * PCOS often presents with the clinical triad of oligomenorrhea and/or anovulation, hirsutism, and obesity. Associated with subfertility and recurrent pregnancy loss. * Rotterdam criteria (2003) states that PCOS diagnosis requires at least two of the following: Oligo- or anovulation (ovulatory dysfunction), hyperandrogenism (clinical and/or biochemical signs), and polycystic ovarian morphology on ultrasound. * Ovaries can be sonographically normal in PCOS. “Hyperandrogenic anovulation” proposed as a more accurate term. * Ovaries can also appear polycystic on ultrasound without clinical diagnosis of PCOS. * Rotterdam description of polycystic ovaries: 12 or more follicles 2-9 mm in size, and/or ovarian volume greater than 10 cc in at least one ovary (with no dominant cysts). * Specific diagnostic cutoffs debated, and 20-25 or more follicles has been more recently suggested as a more accurate cutoff. * Supportive morphologic features of PCOS include the “string of pearls sign” (peripheral location of follicles) and prominent, hyperechoic central ovarian stroma. * Ovarian morphology typically more important than ovarian size, although a single enlarged, polycystic ovary sufficiently meets ultrasound criteria for PCOS. * The term “polycystic” is generally incorrect and “multifollicular” has been offered as a more accurate ultrasound description, but PCOS remains the most widely used term. * In post-menopausal women with new or worsening hyperandrogenism, also consider androgen-secreting tumors of ovaries or adrenal glands. To learn more about the Samsung RS85 Prestige ultrasound system, please visit: https://www.bostonimaging.com/rs85-prestige-ultrasound-system-4 Click the YouTube Community tab or follow on social media for bonus teaching material posted throughout the week! Spotify: https://bit.ly/spotify-rhq Instagram: https://www.instagram.com/radiologistHQ/ Facebook: https://www.facebook.com/radiologistHeadQuarters/ Twitter: https://twitter.com/radiologistHQ Reddit: https://www.reddit.com/user/radiologistHQ/