Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of reproductive age. The ultrasound criteria (Rotterdam 2003, updated 2018) for polycystic ovarian morphology include 20 or more follicles per ovary (2–9 mm in diameter) and/or increased ovarian volume (>10 mL). Follicles are typically arranged peripherally in a “string of pearls” pattern. Transvaginal ultrasound is preferred for accurate follicle counting. PCOS diagnosis requires clinical and biochemical criteria in addition to ultrasound findings.