This study examined factors that influenced undergraduates’ decision to enter,leave,or stay within science majors. In addition,we sought to understand if such decisions differed by gender and type of science major. Using Beginning Postsecondary Students (BPS) longitudinal survey data,we found that women were less likely to select a science major in the first year of college and were less likely to select and persist in science majors after the third year of college compared to males. Women who left science majors after the third year of college selected non-science majors,despite the number of science courses taken within the first two years. One of the most interesting findings was that many students who entered science majors by Year 3 were previously undecided upon entering college. The article concludes with implications for attracting and retaining women in science majors.