Research examining high school and undergraduate students has demonstrated the importance of identity formation for students' confidence, retention, and aspirations in science. While we know some of the key predictors of science identity formation among these populations, relatively little work has looked at these issues among graduate students. The study presented here utilizes data from a survey of over 1,300 graduate students in the United States in five disciplines: biology, chemistry, physics, psychology, and sociology. A structural equation model is estimated to assess the demographic, experiential, and disciplinary correlates of graduate student identification with science and, separately, identification with their discipline. The analysis finds that, relative to men, women have weaker identification with science but do not differ in the strength of their identification with their discipline. Experiences, such as the quality of students' relationship with their advisor and publishing research, are positively associated with the strength of their science and disciplinary identity. Students in psychology and sociology have weaker identification with science relative to biology students, while sociology students also have weaker identification with their discipline.