Background: Prison suicide rates are high, and suicide-related behaviors (SRBs) higher, but effects of contact with such behaviors in prison have not previously been examined. Aims: To compare the mental state of young men witnessing a peer's suicide-related behavior in prison with that of men without such experience, and to test for factors associated with morbidity. Method: Forty-six male prisoners (age 16-21 years) reporting contact with another's suicide-related behavior in prison were interviewed 6 months after the incident, with validated questionnaires, as were 44 without such contact at least 6 months into their imprisonment. Results: Significantly higher levels of psychiatric morbidity and own suicide-related behaviors were found in the witness group, even after controlling for their higher levels of family mental illness and pre-exposure experience of in-prison bullying. Some personal factors were associated with higher morbidity; incident and institutional factors were not. Conclusions: Findings of heightened vulnerabilities among young men exposed to suicide-related behaviors in prison suggest a need for longitudinal study to clarify temporal relationships and inform strategies to prevent or limit development of morbidity and further harm.