We examined possible differences in the factor structure of posttraumatic stress disorder (PTSD) on the basis of whether frequency or intensity symptom response formats were used to assess PTSD. Participants included 669 veterans recruited from an epidemiological study of four Veterans Affairs Medical Centers' primary care clinics in the southeastern United States. Confirmatory factor analysis using measurement invariance testing found that the frequency and intensity symptom formats were significantly different from each other on PTSD's factor structure parameters, including factor loadings, observed variable intercepts, and measurement errors. The only exception was for PTSD's effortful avoidance symptoms, which were associated with equivalent parameter estimates for both the frequency and intensity formats. Implications for the clinical assessment of PTSD and interpretation of the extant literature base on PTSD's factor structure are considered. (Contains 2 tables.)