ABSTRACT That sexual frustration drives foreign fighters into the arms of the Islamic State is a popular hypothesis. Yet the common proxies for sexual frustration ‘male youth unemployment’ and ‘male unmarriedness’ do not square with available and, admittedly, scarce, socio-demographic micro data about foreign fighters. Most foreign fighters were married and employed, but mostly in blue-collar jobs. Often neglected is moreover that most foreign fighters have a migration background. Sexual frustration must therefore not be seen independently from possible socioeconomic frustration. Because strong multicollinearity complicates the empirical separation of sexual and socioeconomic frustration, we employ a principal component analysis to reduce the dimensionality of each frustration. We find that socioeconomic frustration is empirically more dominant, thus lending additional support in favor of the socioeconomic frustration hypothesis and complementing the scarcely existing micro data. Moreover, the results suggest that sexual frustration is a byproduct of socioeconomic frustration, however it is not a significant independent explanatory factor of ISIS foreign fighters.