School plays critical roles in facilitating and inhibiting the safety, development, and well-being of adolescents with T1DM. However, their school-based lived experiences have been under-investigated. This study aimed to explore those experiences for adolescents with T1DM in Taiwan. In conducting the study, Heidegger’s hermeneutic phenomenological approach was used. Fourteen Taiwanese adolescents with T1DM were enrolled between June 2009 and July 2010 through purposive snowball sampling. Data were collected using audio-recorded, semi-structured interviews and analyzed using the hermeneutic circle and West’s (1998) structural analysis steps, supported by qualitative analysis software NVivo 9.0. Reflective journaling, peer debriefing, memo writing, and member checking were performed to enhance the trustworthiness of the findings. Six interrelated themes were identified in the adolescents’ school-based lived experiences. They are (a) the same and different, (b) covert and overt, (c) hyper- and hypoglycemia, (d) independent and dependent, (e) derailing and being on track, and (f) dark clouds and silver lining. In the stressful context of school, the adolescents’ diabetes self-management is challenged. Multiple factors, including unaccepted disease identity; social anxiety and pressure; intrusive, ignorant school personnel and classmates; and transition to independent self-management threaten the adolescents’ health and well-being at school. To optimize diabetes self-management effectiveness, interventions should include the adolescents and their parents, classmates, and school personnel to ease burdens that the adolescents bear. Future interventions should also facilitate the adolescents’ autonomy, self-efficacy, diabetes knowledge and self-management, and capacity to alleviate social pressure. / text