Objective: To assess the inter-rater reliability and concurrent validity of walking speed measurement after traumatic brain injury. Design: Twelve subjects each completed five comfortably paced and five fast-paced walking trials. Walking speed was measured simultaneously by five observers using a stopwatch (clinical procedure) and by infrared timing gates (gold standard). Setting: Brain injury rehabilitation unit. Subjects: People with traumatic brain injury who could walk independently and were participating in a rehabilitation programme. Main outcome measures: Walking speed over a 10-metre distance. Results: The inter-rater reliability of walking speed measured using a stopwatch was very high, with an intraclass correlation coefficient of at least 0.998 for both comfortable and fast-paced tests. Concurrent validity was excellent for comfortable and fast tests, with perfect correlations between the stopwatch and infrared timing gate measurement procedures. Conclusions: Physiotherapists can use a stopwatch as a reliable and valid measurement tool to quantify walking speed over a short distance at both comfortable and fast paces in people who have sustained traumatic brain injuries.