PCOS (named by the appearance of the unruptured follicles in the ovaries -aka cysts- giving the ovaries a chocolate chip cookie appearance) used to be referred to as "syndrome X" or metabolic syndrome. It is now officially referred to as "anovulation" or, absence of ovulation. As TiffyRN said, it is often difficult to find which situation came first, ovarian dysfunction/decreased estrogen production or insulin resistance. Most, but not all women diagnosed with anovulation are overweight and have extreme difficulty losing weight and conceiving. They are NOT diabetic by virtue of being dx'd with anovulation, however "pre-diabetes" aka impaired fasting glucose (above 110 mg/dL in most institutions) is an issue with these women. In the absence of normal levels of circulating estrogen, endogenous androgens are no longer opposed as they would be with normally functioning ovaries. This gives rise to the symptoms of weight gain, hirsutism, abdominal obesity, lethargy, as well as a slew of other s/s. Also, since insulin stores in fat, the more weight gained, the more insulin resistant the tissues become. Metformin increases target tissue sensitivity to insulin allowing blood sugar levels to return to a more normal level, even allowing most individuals to lose some amount of weight, making less fat available for insulin to be stored in. Treatments also include oral contraceptives to take over for the dysfunctioning ovaries that are no longer correctly producing estrogen. What a mess, eh?