Women in the sciences who earn PhDs are less likely than their male counterparts to pursue tenure-track positions at research universities. Moreover, among those who become STEM researchers, men have been found to publish more than women. These patterns raise questions about when sex differences in publication begin. Using data from a survey of doctoral students at one large institution, this study finds that men submitted and published more scholarly works than women across many fields, with differences largest in natural/biological sciences and engineering. Potential contributing factors are considered, including sex differences in faculty support, assistantships, family responsibilities, and career goals.