Purpose: Post-traumatic stress disorder has been reported in survivors of critical illness. The aim of this study was to investigate the predictors of post-traumatic stress disorder in survivors of critical illness. Materials and methods: Patients attending the intensive care unit (ICU) follow-up clinic completed the UK-Post-Traumatic Stress Syndrome 14-Questions Inventory and data was collected from their medical records. Predictors investigated included age, gender, Apache II score, ICU length of stay, pre-illness psychopathology; delirium and benzodiazepine administration during ICU stay and delusional memories of the ICU stay following discharge. Results: A total of 198 patients participated, with 54 (27%) patients suffering with post-traumatic stress disorder. On multivariable logistic regression, the significant predictors of post-traumatic stress disorder were younger age, lower Apache II score, pre-illness psychopathology and delirium during the ICU stay. Conclusions: The predictors of post-traumatic stress disorder in this study concur with previous research however a lower Apache II score has not been previously reported.