BACKGROUND: The stressor criterion (criterion A) in the DSM-IV diagnosis of posttraumatic stress disorder (PTSD) is frequently questioned. To explore the clinical and diagnostic usefulness of criterion A, we examined its value in predicting and capturing PTSD symptom clusters (criteria B-D) in a sample of trauma survivors. METHOD: We studied 342 adult German-speaking Swiss tourists affected by the 2004 tsunami. We analyzed sensitivity and specificity, predictive value and variance explanation of criterion A for evoking PTSD criteria B-D. RESULTS: Sensitivity of criterion A for PTSD criteria B-D was 93.2%, while positive predictive value was 23.1%. Criterion A made a small, yet statistically significant contribution of 7.5% for PTSD symptom clusters B-D. CONCLUSION: The assessment of criterion A (A1 and A2) is not necessary for the identification of individuals suffering from PTSD symptoms according to DSM-IV. We suggest therefore that criterion A is a dispensable part of the diagnosis of PTSD.