This article examines sex segregation in higher education in Norway. The extent to which parent's education and occupation and students' grades have an impact on the choice of male and female dominated subjects is analysed. The analysis uses a framework which integrates socialisation and rational choice perspectives. The data used are from a retrospective survey referring to the autumn of 2000. It was found that grades in mathematics affected the choice of subject field in higher education, but the effect is much stronger among men than women, indicating that rational choice theory serves as a better explanation of the former's behaviour. It was also found that gender atypical choices were most common, among both men and women, if their parents had experienced higher education. Socialisation factors and same-sex influence are important, but the results offer no simple explanation where the youth copies the same-sex parent. (Contains 8 tables and 4 figures.)