Post-traumatic stress disorder (PTSD) comprises four core symptom clusters following a traumatic event: (1) re-experiencing, (2) avoidance, (3) negative cognitions/mood, and (4) hyperarousal, lasting >1 month.(1,2) It causes clinically significant distress or impairment in social, occupational or other important functions.(1) Acute stress disorder (ASD) occurs within 4 weeks of the event and comprises similar symptoms to PTSD, lasting 2 days to 4 weeks.(3,4) Recognition and treatment of PTSD may be complicated by symptom overlap or comorbidity with disorders such as anxiety and depression.(5) Here we discuss recognition of PTSD and evidence for trauma-focused psychological treatment (generally considered to be first-line therapy). Part II of this article will discuss drugs, self-help and complementary therapy options.