Recent international agreement on the definitions of polycystic ovary syndrome (PCOS) has helped to clarify the clinical approach to diagnosis of PCOS. However, in the precise assessment of an individual patient it is still necessary for a detailed history of menstrual disorder (especially oligo- and amenorrhoea and anovulatory dysfunctional uterine bleeding), infertility or miscarriage, hyperandrogenism (mainly acne, hirsutism and scalp hair loss, distinguished from virilization) and obesity supplemented by the demonstration of polycystic ovaries on transvaginal ultrasound scanning. Assessment of endocrine changes in serum levels of luteinizing hormone, follicle stimulating hormone, oestradiol and prolactin, plus appropriate measures of circulating androgens (especially total and free testosterone, sex hormone binding globulin, 17 hydroxy-progesterone, dehydro-epiandrosterone sulphate and sometimes a 24-hour urinary free control) might help in further defining the abnormalities. Assessment of ovulatory status, obesity (body mass index and waist-hip ratio) and insulin resistance (oral glucose tolerance test with serum insulin levels) are also important in most cases. PCOS is a highly variable condition and investigation and management needs to be individualized. Long-term follow-up is also to a great extent dictated by the constellation of symptoms and clinical features of individual patients, but potential long-term hazards should be defined and patients warned of these.