The total duration of ‘ovulatory activity’ or ‘ovulatory age’ has been reported to be the strongest indicator of the risk of ovarian cancer. In the case-control study examined in this paper this variable was found to be a strong correlate of the risk of ovarian cancer. However, the finding that in older women the major determinant of ‘ovulatory age’ was age at menopause (which is a very unreliable indicator of ‘ovarian activity’), and that age at menopause by itself was related to the risk of ovarian cancer as strongly as the total duration of ovulatory age, threw doubt on the biological consistency of that model. Furthermore, the protection conferred by pregnancies was different at different ages, and age at first pregnancy was more strongly associated with the risk of ovarian cancer than the actual number of pregnancies. The model of carcinogenesis for epithelial ovarian cancer appears, therefore, to be more complex than is indicated simply by the total duration of ‘ovarian activity.’