Mild traumatic brain injuries are known to cause a host of symptoms, including headaches, nausea, and depression, that when persistent, are known as postconcussive syndrome. In addition to these overt symptomologies, individuals may experience changes in day-to-day behavior or temperament, which although not meeting criteria for postconcussive diagnosis, does cause distress to the individual. The aim of this study was to determine whether we could measure temperament in a rat and, if so, determine whether temperament is altered in response to repetitive mild traumatic brain injuries (RmTBI). Forty male and female adolescent Sprague-Dawley rats were same-sex pair housed and subjected to RmTBIs or sham injuries. The rats were recorded at 6 different time points throughout the study for the temperament assessment protocol, a measure of the complex behavioral profile of each rat within its dyadic home cage environment. The temperaments were quantified via a novel behavioral scoring algorithm. The rats were also tested on a battery of tests that were designed to measure symptoms of postconcussion syndrome. We determined that rodent temperament is quantifiable, is sex dependent, changes with age, and is modifiable in response to experiential factors such as RmTBI. Rats that received the RmTBIs were significantly less active and showed decreased levels of social interaction compared with their sham-injury counterparts. Moreover, both task switching and recovery patterns for RmTBI rats were dependent on the injury status of their cage mates. Future studies are now required to determine the mechanisms underlying these important changes in temperament.