Post-traumatic stress disorder (PTSD) may develop after exposure to a life-threatening event or serious injury. Symptoms include recurring and intrusive memories, such as flashbacks, avoidance of reminders and persistent symptoms of anxiety or physiological arousal. Many factors are associated with the development of PTSD in intensive care unit (ICU) patients, including increased length of stay, and greater levels and longer duration of sedation. Patient-related factors associated with a higher risk of PTSD include younger age, female gender, previous psychological problems and recall of delusional memories from ICU. In contrast, the formation of even fragmented factual memories may reduce the risk of PTSD. Optimum, analgesia-based sedation may help patients to form factual memories of ICU, so possibly reducing the risk of PTSD. Patient diaries, written by health professionals and family members and close friends, may also support patients in coming to terms with traumatic, delusional memories, and so reduce their emotional and psychological symptoms. Following ICU discharge, validated screening tools such as ICU Memory and Post-traumatic Stress Syndrome 14-Questions Inventory can be used as part of routine follow-up to identify patients who may need referral for more specialist assessment of possible PTSD symptoms.