The measurement of posttraumatic stress disorder (PTSD) is critically important for the identification and treatment of this disorder. The PTSD Checklist (PCL; F. W. Weathers & J. Ford, 1996) is a self-report measure that is increasingly used. In this study, the authors investigated the factorial validity of the PCL with data from 236 cancer survivors who received a bone marrow or stem cell transplantation. The authors examined the fit of these data with the clinical model of 3 symptom clusters for PTSD, as proposed in the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; American Psychiatric Association, 1994), and alternative models tested in prior research. By using confirmatory factor analysis the authors found that a 4-first-order-factor model of PTSD provided the best fit. The relations of PTSD symptoms with sociodemographic and medical variables were also explored.