Does the gender composition in higher education affect student performance and specialization choices? This paper exploits random assignment of students to teaching sections to study the direct, delayed and longer run impact of the peer gender composition in university. Results show small performance increases for females exposed to a higher proportion of female peers and considerable effects for students’ specialization choices. A higher proportion of female peers in compulsory first year courses ‘pushes’ female students away from taking technical/mathematical courses and towards subjects more popular among female students.