Psychological inflexibility, or how individuals respond to distressing internal experiences, may be a modifiable risk factor for suicide in veterans. It was hypothesized that psychological inflexibility would predict suicidal ideation after accounting for established risk factors at baseline and 1 year later. Post-9/11 veterans (N = 309) completed clinical interview and self-report measures at baseline and 1-year follow-up. Results indicated that psychological inflexibility predicted severity of suicidal ideation at both baseline and 1 year later, after accounting for established risk factors. Psychological inflexibility is an important marker of risk for suicidal ideation, and could be a target for interventions aimed at reducing suicide.