Purpose <p>Decision-making is the process of making informed choices about medical treatments and care. This study aimed to synthesize qualitative evidence on adolescents’ lived experiences of decision-making in cancer care, with particular attention to the barriers, facilitators, and emotional dimensions influencing their participation.</p> Methods <p>This study was conducted using the qualitative meta-synthesis methodology outlined by Sandelowski and Barroso (2007). We searched in four databases (PubMed, CINAHL, Embase, and Web of Science) for studies on decision-making in adolescents with cancer. The search period was set from 1989 to April 2023. Eligible studies were peer-reviewed qualitative research on decision-making in cancer care among adolescents; studies focusing only on parents, providers, or clinical trials were excluded. A meta-synthesis was conducted at the quotation-level through iterative discussion and consensus-building.</p> Results <p>We reviewed 18 articles published between 2004 and 2022, involving a total of 343 adolescent participants. Over half were conducted in the United States. Medicine was the most prevalent field, with eight articles, followed by nursing (<i>n</i> = 6). Among the 18 studies, seven articles provided detailed research methods, including three qualitative descriptive studies, three ethnographic studies, and one grounded theory study. The comprehensive meta-synthesis revealed three main categories and seven subcategories: (1) the “I” in decision-making, (2) healthcare environments make decision-making challenging, and (3) attitude toward illness.</p> Conclusion <p>The findings suggest the need to develop adolescent-centered decision-making models and provide ethics-based training for healthcare professionals. Creating supportive care environments that respect adolescents’ autonomy and encourage active participation is also essential.</p>