PURPOSE: We investigated the impact of delirium on illness severity, psychological state, and memory in acute respiratory distress syndrome patients with very long ICU stay. MATERIALS AND METHODS: Prospective cohort study in the medical-surgical ICUs of 2 teaching hospitals. Very long ICU stay (>75days) and prolonged delirium (≥40days) thresholds were determined by ROC analysis. Subjects were ≥18years, full-code, and provided informed consent. Illness severity was assessed using Acute Physiology and Chronic Health Evaluation IV, Simplified Acute Physiology Score-3, and Sequential Organ Failure Assessment scores. Psychological impact was assessed using the Hospital Anxiety and Depression Scale, Impact of Event Scale-Revised, and the 14-question Post-Traumatic Stress Syndrome (PTSS-14). Memory was assessed using the ICU Memory Tool survey. RESULTS: 181 subjects were included. Illness severity did not correlate with delirium duration. On logistic regression, only PTSS-14<49 correlated with delirium (p=0.001; 95% CI 1.011, 1.041). 49% remembered their ICU stay clearly. 47% had delusional memories, 50% reported intrusive memories, and 44% reported unexplained feelings of panic or apprehension. CONCLUSION: Delirium was associated with memory impairment and PTSS-14 scores suggestive of PTSD, but not illness severity.