OBJECTIVE Veterans with a history of mild traumatic brain injury (mTBI) are reporting postconcussive symptoms (PCSx) in addition to experiencing postdeployment physical and emotional comorbidities. The Veterans Health Administration has mandated specialized evaluation and treatment for veterans with a history of mTBI and has suggested widespread use of the Neurobehavioral Symptom Inventory (NSI) as a measure of PCSx. This study evaluated the NSI's factor structure and assessed the impact of posttraumatic stress (PTS) on the scale at the item and factor levels. METHODS Five hundred twenty-nine charts of returning veterans who screened positive for traumatic brain injury were reviewed, and 345 who met criteria for mTBI were included in the study. RESULTS Results of factor analysis on the NSI revealed a difficult-to-interpret factor structure that was inconsistent with the results of civilian studies. PTS explained 5%-38% of the variance in individual PCSx, and after controlling for this variance, the factor structure more closely paralleled findings from the civilian literature. CONCLUSIONS PTS is an important variable to account for when evaluating PCSx in veterans. Research and clinical implications for the measurement and interpretation of self-reported PCSx are discussed.