Predictions about processes linking gender to students' choices of advanced courses were derived from the internal/external frame of reference (I/E) model and expectancy value (EV) theory. The predictions were tested for the domains of mathematics and biology using data from 1,148 students attending academically oriented secondary schools in Germany. Results revealed substantial gender differences on measures gathered in Grade 10. Males outperformed females on the mathematics and biology achievement tests, and reported higher math self-concepts and intrinsic values. Females scored higher on the biology self-concept and intrinsic value scales. Consistent with our expectations, gender differences in Grade 10 mediated the effect of gender on course enrollment in Grade 12. In line with the EV model, self-concepts and intrinsic values had substantial effects on subsequent course choices. As predicted by the I/E model, domain-specific self-concepts and intrinsic values were positively related to course choices in the same domain, but negatively related to choices in the other domain. In addition, results of multigroup structural equation models revealed that the processes underlying course choices were different for males and females. Finally, students' choices of specialized courses were related to their aspired field of college education. (Contains 3 tables, 4 figures and 1 note.)