Prison inmates are exposed to a number of adverse conditions prior to and during incarceration that place them at risk for suicide. The interpersonal theory of suicide may prove useful in better understanding suicide in prisons, allowing for more effective prevention and treatment programs. However, no studies of the interpersonal theory have been conducted in prison populations. Further, there have been no studies examining the factor structure of the assessment of one of the theory's main constructs: the acquired capability for suicide. The current study examined the factor structure of the Acquired Capability for Suicide Scale in a sample of male prison inmates. We found that a 4-factor model provided the best statistical and conceptual fit, though only 3 of these factors were meaningful with an additional method-factor. The 3 resulting factors were each associated with previous exposure to painful and provocative events, but none differentiated suicide attempter status. Results suggest that the interpersonal theory has promise in application to suicide in prison populations, but more work is needed to develop a self-report measure of acquired capability, particularly as it relates to prisoners.