Polycystic ovary syndrome (PCOS) and the concomitant androgen excess may be particularly distressing and disruptive for women. Thus, PCOS requires a prompt diagnosis and adequate treatment. However, the criteria used for diagnosis and definition of PCOS are as heterogeneous as the pathology itself. The advent of ultrasonographic examination of the ovaries has provided the biggest single contribution to the diagnosis of PCOS, having a high concordance rate with laparoscopy and histological examination. In fact, the assessment of ovarian morphology by transvaginal ultrasound and Doppler flow analysis of both intra-ovarian and uterine arteries seems to provide an insight into the pathological state and the degree of progression of the disease, and may be useful in the prevention and management of ovarian hyperstimulation syndrome during ovarian stimulation.