Background: Critical illness can cause post-traumatic stress and impaired mental health. The NONSEDA trial was a Scandinavian multicenter RCT, assessing non-sedation versus sedation with a daily wake-up call during mechanical ventilation in critically ill adults. The aim of this substudy was to assess the effect of non-sedation on post-traumatic stress and mental health. Methods: This substudy is based on all participating patients from a single NONSEDA trial site (Kolding, Denmark). Patients were randomized to sedation or non-sedation within the first 24 hours of mechanical ventilation. Three months after ICU discharge survivors were examined by a neuropsychologist for post-traumatic stress, anxiety and depression, and filled out the SF-36 questionnaire regarding quality of life. Results: The two groups of survivors were similar with regard to baseline characteristics, length of admission and mechanical ventilation. Sedated patients received more propofol and midazolam. Doses of morphine and haloperidole were equal. Primary outcome: the number of patients with post-traumatic stress disorder did not differ between groups (non-sedated: 2 patients vs sedated: 0, P =.23). Secondary outcomes: there were no differences between groups in Beck Anxiety Index (median, non-sedated: 0 vs sedated: 0, P =.62), Beck Depression Index (median, non-sedated: 7 vs sedated: 4, P =.24), SF-36 mental component score (mean, non-sedated: 46.7 vs sedated: 47.5, P =.73) or number of patients with symptoms of post-traumatic stress (8 in both groups, P =.89). Conclusion: Levels of PTSD, anxiety and depression and quality of life regarding mental health were similar between the non-sedated and sedated group.