Objective: To study the relation between posttraumatic stress disorder (PTSD) psychiatric comorbidity and suicidal ideation in a representative sample of Ohio Army National Guard soldiers. Method: Using retrospective data collected on the telephone from a random sample of 2,616 National Guard soldiers who enrolled in a 10-year longitudinal study (baseline data collected November 2008-November 2009), we examined (1) the prevalence of other psychopathologies among those with DSM-IV-diagnosed PTSD compared to those without PTSD and (2) the association between PTSD comorbidity and suicidal ideation (reporting thoughts of being better off dead or hurting themselves). All analyses were carried out using logistic regression. Results: Of guard members with PTSD in the last year, 61.7% had at least 1 other psychopathology; 20.2% had at least 2 other co-occurring conditions. The most common co-occurring psychopathology was depression. While those with PTSD overall were 5.4 (95% CI, 3.8-7.5) times more likely to report suicidality than those without PTSD, those who had at least 2 additional conditions along with PTSD were 7.5 (95% CI, 3.0-18.3) times more likely to report suicidal ideation at some point in their lifetime than those with PTSD alone. Conclusions: Soldiers with PTSD were at increased risk for suicidality, and, among those with PTSD, those with at least 2 additional conditions were at the highest risk of suicidal ideation. Future research should address the mechanisms that contribute to multimorbidity in this population and the appropriate treatment methods for this high-risk group.