Whereas past research has demonstrated the relationship between posttraumatic stress disorder (PTSD) and criminal behavior, the present study examines the underlying mechanisms driving this association. The primary objective was to determine the role of psychopathy and suicidal ideation as mediating factors in the relationship between military PTSD symptoms and criminal behavior (defined as incarceration status). A correlational study using archival data from the U.S. Disciplinary Barracks (USDB) and a control population of U.S. Army soldiers was conducted. The USDB provided data from 310 incarcerated male U.S. Army soldiers. Data were also collected from 310 nonincarcerated, male U.S. Army soldiers in the greater Fort Rucker, Alabama area. Data validity checks eliminated some cases, thus yielding a final dataset of 246 USDB and 252 control participants. The results suggested partial mediation, in that PTSD symptoms had a direct effect on incarceration status, and significant indirect effects through suicidal ideation and psychopathy while controlling for intelligence and warmth. In furnishing evidence of how psychopathy and suicidal ideation mediate the relationship between PTSD and incarceration status in military personnel, this research highlights specific internalization and externalization mechanisms that may increase the tendencies of people with greater PTSD symptoms to engage in criminal behaviors. By adding to the small amount of prior research on why PTSD sometimes leads people to engage in criminal behaviors, our research provides specific, observable symptoms that clinicians may use to identify, treat, and possibly ameliorate facets of PTSD that can lead affected people to engage in criminal behaviors.