Ten women with cystic fibrosis (CF) were evaluated with regard to hormonal profiles during a natural and a clomiphene citrate (CC) stimulated cycle. Five of the women were found to be anovulatory during a natural cycle. All women except one did respond with ovulation to CC stimulation indicating adequate ovarian response. Neither did they show increased follicle-stimulating hormone (FSH) concentrations on day 10 after CC treatment confirming normal ovarian reserve. Clinically the anovulatory women differed from the ovulating in two aspects: more profound essential fatty acid deficiency (EFAD) and higher peak/basal insulin response during an oral glucose tolerance test. The anovulatory women had significantly lower luteal oestradiol and progesterone but higher total testosterone concentrations when compared to healthy controls and the ovulatory CF women. The pathological insulin response and high testosterone concentrations resemble those seen in women with polycystic ovarian (PCO) syndrome. However, the CF patients in our study had normal ovaries, as deduced from ultrasound examination and normal luteinizing hormone (LH)/FSH ratio. It is suggested that EFAD as well as hypersecretion of insulin may be of importance for the observed ovarian dysfunction. Further studies are needed to evaluate the relation between ovulatory mechanisms and EFAD in CF women as well as studies to compare anovulatory CF women with women with PCO syndrome.