Rationale: Intensive care unit (ICU) admission of a relative is a stressful event that may cause symptoms of post-traumatic stress disorder (PTSD). Objectives: Factors associated with these symptoms need to be identified. Methods: For patients admitted to 21 ICUs between March and November 2003, we studied the family member with the main potential decision-making role. Measurements: Ninety days after ICU discharge or death, family members completed the Impact of Event Scale (which evaluates the severity of post-traumatic stress reactions), Hospital Anxiety and Depression Scale, and 36-item Short-Form General Health Survey during a telephone interview. Linear regression was used to identify factors associated with the risk of post-traumatic stress symptoms. Main results: Interviews were obtained for family members of 284 (62%) of the 459 eligible patients. Post-traumatic stress symptoms consistent with a moderate to major risk of PTSD were found in 94 (33.1%) family members. Higher rates were noted among family members who felt information was incomplete in the ICU (48.4%), who shared in decision making (47.8%), whose relative died in the ICU (50%), whose relative died after end-of-life decisions (60%), and who shared in end-of-life decisions (81.8%). Severe post-traumatic stress reaction was associated with increased rates of anxiety and depression and decreased quality of life. Conclusion: Post-traumatic stress reaction consistent with a high risk of PTSD is common in family members of ICU patients and is the rule among those who share in end-of-life decisions. Research is needed to investigate PTSD rates and to devise preventive and early-detection strategies.