One patient had been treated as having PCOS because she had irregular periods and her ovaries had polycystic-like changes on ultrasound. When the pregnancy turned out to be inevitably miscarried, it was discovered that the real cause was hypothyroidism. With this case I would like to talk about polycystic ovary syndrome (PCOS) and polycystic change of ovaries (PCO). Polycystic ovary syndrome (PCOS) and polycystic ovarian change (PCO) are two different concepts. The authoritative book on gynecology, Chinese Obstetrics and Gynecology, states: “PCO is only a morphological sign. In addition, about 20% of normal women without clinical symptoms have PCO signs during ultrasound examination. PCOS refers to a series of manifestations such as menstrual disorders, persistent ovulation disorders, hyperandrogenemia, and ovarian polycystic changes caused by excessive androgen production due to benign proliferation of ovarian follicular cells with onset around puberty.” Therefore, when your ovaries have polycystic-like changes during ultrasound examination, do not diagnose polycystic ovary syndrome (PCOS) easily, but make sure to find out the cause and diagnose and treat it correctly.