This manuscript begins by reviewing the literature concerning the use of the SCID versus the PCL for diagnosing PTSD, and by reviewing the literature regarding the presence of suicidal ideation as a clinical correlate of PTSD. This manuscript then describes our recent study involving PTSD among Veterans, which assessed the presence of suicidal ideation as a clinical correlate of PTSD, as diagnosed by the SCID versus as diagnosed by the PCL. We hypothesized that the presence of suicidal ideation would be associated with a diagnosis of PTSD. Subjects were 101 Veterans recruited from VA behavioral health and substance use treatment clinics in the VA Pittsburgh Healthcare System. The study compared correlations of suicidal ideation with PTSD as determined with the PTSD Checklist versus the Structured Clinical Interview for DSM-IV, and utilized question 9 of the Beck Depression Inventory for assessing presence of SI. PTSD was diagnosed in 15 subjects using the SCID, and in 15 subjects using the PTSD Checklist. SI were reported by 16 subjects. The presence of SI was significantly associated with the diagnosis of PTSD on the PCL (chi-square=5.73, df=1, p=0.017) but not on the SCID (chi-square=0.08, df=1, p=0.773). These findings suggest that SI associated with the diagnosis of PTSD among Veterans are better ascertained by the PCL as compared to the more elaborate diagnostic algorithm used in the SCID. The current study finding raises the possibility that a less complicated diagnostic assessment instrument such as the PCL may be superior to the SCID, a more complicated instrument for diagnosing PTSD, at least in some populations.