There are fewer female than male professors in the world (21–79 distribution in the country of examination). The unequal distribution of male and female professors has usually been taken to indicate that men and women have not had equal opportunities to achieve professorship. At the same time, the increase in the proportion of female professors has been taken as evidence that academia is becoming more gender equal. It is possible that both of these assumptions are flawed, and that the gender distribution among professors is the result of demographic inertia, i.e., affected by the previous distribution of men and women within the system, and how fast the distribution has changed.This study examines whether the chances, for men and women, of becoming a full professor changes over time, and whether gender differences may possibly depend on early career events. It concludes that women are significantly less likely than men to become professors and that this situation is not improving over time. In spite of policies that have tried to increase the proportion of female professors, the chances of a woman becoming a professor do not change over time. We also show that these gender differences in promotion rate can be attributed to early career events.