Sleep disturbances reflect a core dysfunction underlying Posttraumatic Stress Disorder (PTSD). Specifically, disruptive nocturnal behaviors (DNB) may represent PTSD-specific sleep disturbances. The Pittsburgh Sleep Quality Index Addendum for PTSD (PSQI-A) is self-report instrument designed to assess the frequency of seven DNB. The goal of this study was to examine the psychometric properties of the PSQI-A to characterize DNB in a group of participants with and without PTSD. Results indicate that the PSQI-A has satisfactory internal consistency and good convergent validity with two standard PTSD measures even when excluding their sleep-related items. A global PSQI score of 4 yielded a sensitivity of 94%, a specificity of 82%, and a positive predictive value of 93% for discriminating participants with PTSD from those without PTSD. The PSQI-A is a valid instrument for PTSD applicable to both clinical and research settings.