Objective: To determine the relationship of postconcussion symptoms (PCS) with functional outcome measures at 6 months postinjury and severity measures at the time of the injury in patients with traumatic brain injury (TBI). Design: Inception cohort study. Setting: Initial setting was Trauma I hospitals with community as primary follow-up setting. Participants: Patients (N = 393) presented with TBI to emergency department of Trauma I hospitals with follow-up at 6 months. Glasgow Coma Scale (GCS) scores were available for 366 patients with mild (N = 167), moderate (N = 33), and severe (N = 166) TBI. Subjects were aged 16 years or older, mostly men (68%) with an average age of 36.8 years (SD = 17.7) and a median age of 32 years. Interventions: Not applicable. Main outcome measures: GCS and length of stay (LOS) in intensive care unit were obtained from hospital records. Rivermead Post Concussion Symptoms Questionnaire (RPCSQ), Functional Status Examination (FSE), and Glasgow Outcome Scale- Extended (GOS-E) were administered by mail, telephone, or in person at 6 months postinjury. Results: Global endorsement of current PCS was trivially correlated with GCS or LOS, although RPCSQ scores increased nonsignificantly over severe, moderate, to mild GCS categories. Current PCS was moderately correlated with FSE (r = 0.45) and GOS-E (r = -0.38) (Ps <= .001), whose scores showed reduced functioning and lower moderate disability, respectively. Conclusions: PCS were endorsed at 6 months postinjury, regardless of TBI severity with minimal global increase of symptoms from severe to moderate to mild TBI. In contrast, current endorsement of global PCS showed moderate correlation with several outcome measures with greater endorsement of PCS associated with poorer adaptive functioning.