Women remain underrepresented in the STEM workforce. We assess explanations for women's underrepresentation in STEM jobs, focusing on a cohort that came of age in the 1980s and 1990s, when women dramatically increased their representation in the scientific labor force. Data are from the NLSY79, and our analysis focuses on members of this cohort who received a college degree, with an emphasis on those who completed a degree in a STEM field. Our analyses test the extent to which college major, expectations to work in STEM, and family expectations shaped transitions into STEM occupations within two years of degree completion. Among those majoring in STEM fields there were no gender differences in transitioning into STEM jobs, though there were sizable differences in transitions to STEM employment by field of study. Of note are gender differences in associations between family expectations and transitions into STEM employment. The most career oriented women, who expected to marry late and limit fertility, were no more likely to enter STEM jobs than were women who anticipated marrying young and having two or more children. The men most likely to enter STEM occupations, in contrast, adhered to significantly more conventional gender ideologies than their female counterparts, expecting to marry at younger ages but also to remain childless. Results of our regression decomposition indicated that marriage and family expectations and gender ideology worked in opposite directions for men and women. Nonetheless, the majority of the gender disparity in transitions into STEM jobs was related to women's underrepresentation in engineering and computer science fields of study. [ABSTRACT FROM AUTHOR]