PRIMARY OBJECTIVES: To evaluate irritability following traumatic brain injury.RESEARCH DESIGN: A prospective study was conducted at a level I trauma centre. METHODS AND PROCEDURES: One hundred and forty-four participants, which included 80 healthy subjects and 64 patients suffering from TBI, were recruited. Irritability was assessed by the National Taiwan University Irritability Scale (NTUIS) from patients themselves and their families. MAIN OUTCOMES AND RESULTS: the results showed 14.8% of patients and 29.4% of their families reported patients' problems of irritability. Meanwhile, both self-reported and family-reported irritability post-injury were significantly higher than those reported by the healthy subjects. When evaluating two sub-components of irritability, respectively, both family- and self-reported post-injury annoyance were significantly higher than the pre-injury one, while the self-reported post-injury verbal aggression was not.