Veterans are at a greater risk for suicide compared to the general population. Suicide risk further increases for veterans with posttraumatic stress disorder (PTSD). The Interpersonal Psychological Theory of Suicide (IPTS) states that a combination of higher perceived burden and lower thwarted belonging increases risk for suicidal ideation (SI), and when SI is present, higher acquired capability for suicide (ACFS) increases risk for suicide attempt. The IPTS is well supported in samples of the general population, but understudied in military samples. The current study tested the IPTS, using PTSD severity in place of perceived burden, and bothersomeness of negative social support (BNSS) and satisfaction of positive social support (SPSS) in place of thwarted belonging, and the original measure of ACFS in 290 military service members/veterans. We observed that higher PTSD and BNSS and lower SPSS were associated with SI and higher suicide risk. BNSS demonstrated a nearly equivalent association to both SI and total suicide risk compared to SPSS. Neither the combined effect of PTSD severity and BNSS/SPSS on SI nor the combined effect of PTSD severity, BNSS/SPSS and ACFS on suicide risk were significant. Findings suggest that PTSD and SPSS/BNSS may not be useful variables for testing the IPTS, but that they are useful individually to assess suicidal behavior. Moreover, given the nearly equivalent association of BNSS and SPSS with suicide risk observed in the current study, clinicians and researchers should attend to both the positive and negative facets of social support in place of measuring only aspects of positive social support.