The role of the source of discrimination in relation to minority Muslim youths' psychosocial well-being has received remarkably little attention in the post-9/11 climate. We have examined one of the aspects of psychosocial well-being that is given prominent attention in the media and public discourse, namely externalising behaviour. The article reports whether perceived discrimination by four sources (school peers and teachers, peers, and adults outside the school) is related to externalising behaviour. Links between perceived discrimination sources and externalising behaviour among Dutch Muslim youths (n = 308, ages 14-18) were examined through surveys. The quantitative findings guided our qualitative analyses of interviews with 10 Muslim Dutch youths on their accounts of discrimination in the school context. When comparing different discrimination sources, only teacher discrimination was found to predict externalising behaviour significantly (explaining 15% of the variance). The qualitative follow-up illustrated the significance of teacher discrimination: Some Muslim youths felt that their teachers held back their school progress, while others reported receiving insults from teachers about their parents' native country and their religion. We argue that students' perceived powerlessness within the teacher-student relationship deserves further attention, as some Dutch Muslim youths reported painful experiences, with perceived teacher discrimination linked to higher levels of externalising behaviour.