Screening asymptomatic women in the general population for 'early ovarian ageing' will be more effective in high-risk groups. Recent findings support the hypothesis that women with polycystic ovaries (PCO) may have actually been born with a larger pool of resting follicles. The mechanism is almost certainly genetic and occurs in fetal life. If, as is widely accepted, the rate of depletion of the ovarian reserve depends primarily on the size of the remaining pool of small follicles, women with PCO will be unlikely to undergo an accelerated depletion of their follicle pool, normally seen in the late thirties, significantly earlier. In terms of asymptomatic screening for early ovarian ageing in the general population, women with PCO constitute a low-risk group and should therefore be excluded.