The aim of this prospective study was to explore the predictors for the development of PTSD in police officers six months after encountering situations of a potentially traumatic nature. Fifty-nine police officers were studied immediately after the event (T1) and six months later (T2). At T2 PTSD was assessed using the Structured Clinical Interview for DSM-IV (SCID-I). PTSD was predicted by intrusions (Impact of Event Scale-Revised; IES-R), the impairment scale (is), global assessment of functioning scale (GAF), gender, age and sense of coherence scale (SOC). The diagnosis of an acute stress disorder (ASD) at T1 had a high specificity for identifying PTSD at T2. The strongest predictor for the development of PTSD was found to be the factor intrusions. Contrary to our expectations, age was not a significant predictive factor for PTSD. Thus, acute stress disorder (ASD) and a high degree of intrusions experienced immediately after a traumatic incident helped to identify early police officers at risk of developing chronic PTSD.