The aim of the study was to assess the impact of temperament and trauma considered as predictors of PTSD experienced under flood. Two samples were studied. In the first one composed of 384 subjects PTSD was assessed three and 15 months (N = 321) after flood. In the second sample (N = 378) PTSD was assessed two years after disaster and retrospectively few weeks after flood. For measuring PTSD the PTSD – Factorial Version Inventory constructed by the authors was administered. Apart from a total score the PTSD-F allows for assessing intrusion/hyperarousal (I/H) and avoidance/numbing (A/N). Three temperamental traits were selected for the purpose of this study – emotional reactivity, briskness and perseveration measured by the Formal Characteristics of Behavior – Temperament Inventory. Intensity of trauma was assessed via structured interview. For analyzing the data coefficients of correlation and hierarchical regression were introduced. It came out that the impact of temperament and trauma as predictors of PTSD is stronger for long-term PTSD. Several interactions between trauma and temperament were obtained. Trauma and emotional reactivity are the best predictors and this refers to the total score of PTSD as well as to the two basic factors – I/H and A/N.