Polycystic ovary syndrome (PCOS) is a heterogeneous disorder of unexplained hyperandrogenic chronic anovulation. Experts have recommended including the morphology and volume of the ovary in the diagnostic criteria for PCOS. We performed this study to determine whether there was an association between the morphology and size of the ovaries and markers of insulin sensitivity as determined by dynamic testing within women with PCOS or compared with a group of control women. We then examined reproductive parameters. We studied 88 unrelated PCOS women and 21 control women, aged 17-45 yr. All were in the early follicular phase or its equivalent (no follicle with > 10 mm diameter and anovulatory serum progesterone level < 3 ng/ml). Subjects underwent on the same day a phlebotomy for baseline hormones, a 2-h oral glucose tolerance test, and transvaginal ultrasound to determine the morphology and volume of the ovaries. Ninety-five percent (84 of 88) of women with PCOS and 48% (10 of 21) of the control women had polycystic ovaries using the criteria of at least one ovary greater than 10 cm3 (PCOV) and/or polycystic ovary morphology (PCOM) using the criteria of 10 or more peripheral follicular cysts 8 mm in diameter or less in one plane along with increased central ovarian stroma. PCOM was a better discriminator than PCOV between PCOS and control women. The odds of women with PCOS having PCOM were elevated 50-fold compared with controls (odds ratio, 50; 95% confidence interval, 10-240; P < 0.0001), whereas the odds of PCOV were elevated 5-fold in women with PCOS (odds ratio, 4.6; 95% confidence interval, 1.7-12.6; P = 0.003). Neither the insulin sensitivity index, fasting or 2-h values, or any integrated measures of glucose and insulin varied in women according to either morphology or volume, nor was there an association with circulating androgen levels. Women with PCOS and PCOM had lower FSH levels than women with PCOS and non-PCOM. Women with PCOS and PCOV had a higher LH to FSH ratio than women without PCOV and PCOS. These data support the hypothesis that polycystic ovaries are an abnormal finding. However, neither the morphology nor the volume of the ovaries is associated with distinctive metabolic or reproductive phenotypes in women with PCOS.