Objective Many people who think about suicide do not engage in suicidal behavior. Identifying risk factors implicated in the process of behavioral enaction is crucial for suicide prevention, particularly in high-risk groups such as prisoners. Method Cross-sectional data were drawn from a nationally representative sample of 17,891 prisoners (79% men) in the United States. We compared prisoners who attempted suicide (attempters; n = 2,496) with those who thought about suicide but never made an attempt (ideators; n = 1,716) on a range of established risk factors. Results More than half (59%) of participants who experienced suicidal ideation had also attempted suicide. Violent offending, trauma, brain injury, alcohol abuse, and certain mental disorders distinguished attempters from ideators. Conclusion Our results fit within recent ideation-to-action theories that emphasize the role of a capability for suicide in the transition from thoughts to acts of suicide.