Objectives: Investigate knowledge of CF in a teenager population and compare this between 2 groups: adolescents with a fellowstudent with CF (“CF-class”) and a group without a fellowstudent with CF (“Non-CF-class”). We hypothesise that CF-class adolescents have better knowledge of CF disease compared to Non-CF-class students. Methods: A questionnaire (Q) to determine the knowledge of CF was developed and distributed among different schools after obtaining informed consent.Written Qs contained 6 demographic and 12 knowledge questions, giving three possibilities: Y/N/I don’t know. Results: In total, 359 completed Qwere obtained: 135 (37.6%) CF-class; 224 (62.4%) Non-CF class. Overall knowledge of CF was belowaverage (Mean in percentage (M) = 42.17%, SD = 3.92). Students in a CF-class have better knowledge of CF than Non-CF class students [M = 50.33% (SD = 3.95) vs M= 37.17% (SD = 3.79), p < 0.001]. Overall, 50.42% of teenagers have heard of CF, surprisingly only 65.18% of CF class students actually have. In 28.89% of the cases a fellow student in the CF-class indicates not to knowanybody with CF. Overall, 34.54% knows someone with CF; 49.44% knows that CF is not contagious and 53.63% knows that CF patients need follow-up in a specialised CF centre. More than 90% of the respondents, both in the CF (92.59%) and Non-CF class (94.19%), do not know that CF is incurable. Almost half of the teenagers (47.9%) indicate that their knowledge of CF is poor. Conclusion: Knowledge of CF is low in general in the teenage population. Adolescents with a fellowwith CF in their class have better knowledge than those without. However, almost one third of fellow students in a CF class decline that they knowsomeone with CF, suggesting that not all CF patients inform their peers about their illness. Future research should focus on the reasons why CF-teenagers withhold their diagnosis and whether mental well-being of CF-students in general would improve if knowledge among peers would increase.