The increasing numbers of aging prisoners raise the issue of how they maintain their personal identity and self-esteem in light of long-standing detention. This study sought to answer this question since identity and self-esteem could influence mental and physical health. We conducted a secondary analysis of 35 qualitative interviews that were carried out with older inmates aged 51-75 years (mean age: 61 years) living in 12 Swiss prisons. We identified three main themes that characterized their identity: personal characterization of identity, occupational identity, and social identity. These main themes were divided into sub-themes such as familial network, retirement rights or subjective social position. Personal characterization of identity mostly happened through being part of a network of family and/or friends that supported them during imprisonment and where the prisoner could return to after release. Individual activities and behavior also played an important role for prisoners in defining themselves. Occupational identity was drawn from work that had been carried out either before or during imprisonment although in some cases the obligation to work in prison even after reaching retirement age was seen as a constraint. Social identity came from a role of mentor or counselor for younger inmates, and in a few cases older prisoners compared themselves to other inmates and perceived themselves as being in a higher social position. Identity was often expressed as a mix between positive and negative traits. Building on those elements during incarceration can contribute to better mental health of the individual prisoner which in turn influences the chances for successful rehabilitation.