This article explores the challenges local youth workers face at the intersection of providing social care and detecting violent extremism. Extremism and other radical ideologies are often assumed to be a harbinger of terrorism. Even though both are still a rare phenomenon among adolescents, European states have become highly concerned with being alert to early signs of radicalisation processes. As a result, youth workers as well as other local professionals have been confronted with the task of detecting these early signs. However, despite training and increased knowledge, the question remains whether youth workers are sufficiently equipped to assess potential risks in youth who show no concrete plans for criminal action. In these cases, prevention targets ideas rather than violent behaviour. This article details qualitative results of a case study among Dutch youth workers and suggests that no clear framework exists for detection of radicalisation processes into (violent) extremism. This has two main causes. Firstly, the concepts of radicalisation and (violent) extremism are in practice difficult to distinguish. Secondly, the youth worker's judgement often relies more on individual perceptions rather than evidence-based criteria to identify potential ‘risky’ persons. This situation may lead to undesired side effects such as executive arbitrariness, prejudice or stigmatisation.