The present study was designed to evaluate whether there is a lower pregnancy rate in women with short follicular phases, as defined by attaining the peak estradiol level before day 11 of the cycle. Thirty-two early ovulators with mature follicles were matched with 32 women being treated for similar infertility problems, who ovulated between days 12-20. Pregnancies were achieved by 9 (28.1%) of the early ovulators compared to 19 (59.4%) of the controls. The mean number of cycles required to achieve a pregnancy was 8.6 in the early ovulators compared to 6.4 in the controls. Using the clinical life table method, the 12-month pregnancy rate was estimated to be 31.4% for early ovulators as compared to 66.3% for controls. Whether lengthening the follicular phase by drug treatment will improve pregnancy rates remains to be seen.