Background: Rates of suicide and suicide-related behavior (SRB) are high in prison. Those witnessing such behavior may develop psychological morbidity. Most previous studies have been quantitative. Little has been written about the witnesses' qualitative experience. Aims: The aim of the study was to explore, through interview and then thematic analysis, the core concerns of those witnessing another's SRB in prison. Method: We interviewed 70 detained young men about their experience of another's SRB in prison. Results: Three main themes were identified: their experience of another's SRB; their thoughts of why the victim died by/attempted suicide; and the physical, emotional, and cognitive effects of another's SRB on them. Responses to questions about the witnesses' experience of support from others, unmet needs, and peers' responses are also described. Two categories within the theme "thoughts of why the victim died by/attempted suicide" were associated with being in prison, all others could be experienced in the community. Over half of the sample reported negative reactions to witnessing another's SRB. Conclusion: Most themes were unrelated to prison. Though many reported negative reactions to their experience, suggesting a need for support, many denied that need. The implication of this study is that prison discipline and health-care staffneed to consider how to provide needed support and care in an acceptable form to young men in prison.