Introduction: Moped riders have a comparably high risk of getting seriously injured or killed in road traffic crashes. The moped is the first motor vehicle legally available to adolescents, but knowledge about young moped riders is limited. The few existing studies indicate that violations are a key factor in crash involvement. Method: Using the Theory of Planned Behaviour, the purpose of this study is to explore and identify key beliefs underlying engagement in violations among adolescent moped riders. We conducted four focus groups including 35 participating adolescents aged between 15 and 17. We analysed the data using a four step directed content analysis approach. Results: Engagement in violations was associated with affective and functional advantages such as excitement, saving time, convenience and avoidance of expenses and parent involvement. Level of approval varied across violations and was expressed directly as well as indirectly by both parents and peers. Strong beliefs in good riding skills and the ability to keep control over the moped facilitated engagement in violations. Actual and expected apprehension by the police was the main barrier, thus preventing engagement in violations. Conclusion: Advantages associated with engagement in violations, approval from peers, parents and general society, and a strong belief in the ability to avoid negative consequences facilitate engagement in violations among young moped riders. Inclusion of the identified beliefs in preventive measures is discussed.