OBJECTIVE: The Extended Glasgow Outcome Scale (GOS-E) is used for objective assessment of functional outcome in traumatic brain injury (TBI). In situations where face-to-face contact is not feasible, telephonic assessment of the GOS-E might be desirable. The aim of this study is to assess the level of agreement between face-to-face and telephonic assessment of the GOS-E. SETTING: Multicenter study in 2 Dutch University Medical Centers. Inclusion was performed in the outpatient clinic (face-to-face assessment, by experienced neurologist), followed by assessment via telephone of the GOS-E after ±2 weeks (by trained researcher). PARTICIPANTS: Patients ±6 months after TBI. DESIGN: Prospective validation study. MAIN MEASURES: Interrater agreement of the GOS-E was assessed with Cohen's weighted κ. RESULTS: From May 2014 until March 2018, 50 patients were enrolled; 54% were male (mean age 49.1 years). Median time between trauma and in-person GOS-E examination was 158 days and median time between face-to-face and telephonic GOS-E was 15 days. The quadratic weighted κ was 0.79. Sensitivity analysis revealed a quadratic weighted κ of 0.77, 0.78, and 0.70 for moderate-severe, complicated mild, and uncomplicated mild TBI, respectively. CONCLUSION: No disagreements of more than 1 point on the GOS-E were observed, with the κ value representing good or substantial agreement. Assessment of the GOS-E via telephone is a valid alternative to the face-to-face interview when in-person contact is not feasible.