In the human ovary, expression of anti-Müllerian hormone (AMH) is detected primarily in granulosa cells of preantral and small antral follicles. The aim of this study was to compare serum AMH measurements in obese women with polycystic ovary syndrome (PCOS) with those in obese normo-ovulatory women and to evaluate the role of AMH as a predictor of ovulation induction by clomiphene citrate compared to FSH. Sixty-eight obese women with PCOS were compared to 17 normoovulatory obese women. All women had a body mass index greater than 30 kg/m(2). Women with PCOS received clomiphene citrate (150 mg/day) for 5 days starting from day 3 of cycle and were subdivided into responsive and non-responsive groups. There was a significant difference in AMH concentration between women with PCOS and the control group (P < 0.05) and also between women with PCOS who responded to clomiphene citrate and those who did not (P < 0.01). A value of 1.2 ng/ml AMH could be used to predict response to clomiphene citrate in obese women with PCOS (sensitivity 71%, specificity 65.7%). AMH production increases in women with PCOS compared to controls. AMH measurement could also be useful in the prediction of ovarian response to clomiphene citrate.