Objective: To assess which social activities were still impaired 5 years after a traumatic brain injury (TBI) in adults, and which neuropsychological impairments were associated with this loss of social autonomy. Design: Cross-sectional study of 79 patients selected from the follow-up cohort of an epidemiologic survey of 2,116 TBI patients. Setting: The present study was of ambulatory patients seen at hospital or at their homes. The inception cohort was from the trauma center of a university hospital and from a general hospital that is representative of level II trauma centers in Aquitaine, France. Patients: Seventy-nine patients selected from a representative sample of 407 patients who were included in the 5-year follow-up study of the initial cohort (convenience sample). Main Outcome Measures: Glasgow Outcome Scale (GOS) and loss of social autonomy as assessed by the European Brain Injury Society's European Head Injury Evaluation Chart; assessment of neurobehavioral impairments by means of the Neurobehavioral Rating Scale-Revised. Results: Up to 16 patients suffered disability for at least one social skill because of cognitive/behavioral reasons. Seven needed full-time supervision. Performing administrative tasks and financial management, writing letters and calculating, driving, planning the week, and using public transport were the most impaired social abilities. Loss of social autonomy was mainly observed in severely injured patients. Univariate analysis showed that mental fatigability, motor slowing, memory difficulties, and disorders of executive function were associated with low scores on the GOS, unemployment, and difficulties in shopping, using public transport, and performing financial management and administrative tasks. Conclusion: Persistent impairments of executive functions and speed of psychomotor processing are major factors associated with loss of social autonomy and inability to return to work long after TBI in adults. Improving these impairments in concrete social situations represents a major challenge for cognitive rehabilitation.