Objective: To describe the interactions between incarcerated adolescents and their grandparents during the processes of living and ageing. Method: An exploratory, descriptive, qualitative study was carried out, based on a semi-structured interview with 11 adolescents aged from 17 to 20 incarcerated in a youth detention center in the state of Rio Grande do Sul, Brazil. The discourse of the adolescents was analyzed based on content themes. Results: Categories that were both intertwined and complete among themselves were constructed: a) grandparents as affective support for incarcerated adolescents and b) relationships of reciprocity and healthy coexistence between the adolescents and their grandparents. Conclusion: The results showed that despite relational conflicts, the participants perceived the role of their grandparents in their lives as beneficial, as they offer a familial reference space, providing shelter and affection against the anxieties of the adolescents and those related to their families. This form of coexistence was a potential part of the development of young people in conflict with the law, and a favorable environment of mutual exchanges and learning, and as figures continuing the transgenerational family culture. Family separation was mentioned as a recurring and underreported process in the lives of adolescents and their grandparents.