The short answer
PCOS (polycystic ovary syndrome) is a clinical diagnosis requiring at least two of three Rotterdam criteria: irregular cycles, clinical or biochemical androgen excess, and polycystic ovarian morphology on ultrasound. Polycystic ovarian morphology (PCOM or sometimes informally 'PMOS') refers only to the ultrasound finding of multiple small follicles and is present in up to 25% of women without any syndrome—having it alone does not equal a PCOS diagnosis.
Defining the terms
PCOS is a syndrome—a cluster of signs and symptoms. Polycystic ovarian morphology (PCOM) is one possible component of that syndrome but can exist in isolation in women with regular cycles and normal androgens. The confusion arises because older terminology used 'polycystic ovaries' loosely for both the morphology and the syndrome. Current guidelines (Rotterdam 2023) prefer 'PCOM' for the ultrasound finding and reserve 'PCOS' for the full syndrome.
Why the distinction matters for diagnosis
Being told you have 'polycystic ovaries' on an ultrasound without meeting other criteria does not mean you have PCOS and should not trigger treatment for it. Conversely, some people with PCOS have normal-appearing ovaries on ultrasound. A formal diagnosis requires clinical assessment by a qualified healthcare professional, not imaging alone.
Quick follow-up questions
Should I be treated for PCOS if I only have the ovarian morphology?
Not necessarily. PCOM without other PCOS criteria does not require hormonal or metabolic treatment. Discuss with your gynaecologist or endocrinologist whether any monitoring or lifestyle advice is appropriate for you.