Irritability is not uncommon after traumatic brain injury (TBI). Unfortunately, no instruments are available to directly measure this clinical feature. This study thus aimed to develop a specific scale to evaluate the irritability for patients with TBI. A total of 144 participants, which include 80 healthy participants and 64 patients suffering from TBI, were recruited. Irritability was assessed by the National Taiwan University Irritability Scale (NTUIS). Our results showed the NTUIS has good reliability. The factor analysis further revealed 2 different components: annoyance, and verbal aggression. Moreover, both self-reported and family-reported irritability postinjury were significantly higher than the irritability reported by the healthy participants. Indeed patients with TBI have significant problems with irritability after injuries, and thus a more specific assessment tool to carefully evaluate patients' irritability should be used.