OBJECTIVE: Posttraumatic stress disorder (PTSD) is associated with high rates of psychiatric comorbidity. Existing theories consider comorbidity as a consequence of PTSD (model 1), PTSD and comorbidity as a consequence of shared factors of vulnerability (model 2), and comorbidity as a consequence of trauma-type specific mechanisms (model 3). METHOD: To compare the explanatory value of these models, we assessed PTSD (model 1), sense of coherence (model 2) and satisfaction with health (model 3) and symptoms of anxiety and depression as indicators of comorbidity 5 days (t1) and 6 months (t2) postaccident in 225 injured accident survivors. Structural equation models representing models 1 to 3 were tested separately and combined. RESULTS: Combined, models 1 and 3 explained 82% of the variance of comorbid symptoms at t2. Posttraumatic stress disorder and satisfaction with health (t2) exerted strong influences on comorbid symptoms. CONCLUSION: Comorbidity besides PTSD is best described by an integration of competing explanatory models.