Traumatic brain injury (TBI) often presents with co-morbid depression and elevated levels of boredom. We explored the relationship between boredom and depression in a group of mild (n
= 38), moderate-to-severe TBI patients (n
= 14) and healthy controls (n = 88), who completed the Beck Depression Inventory and Boredom Proneness Scales as part of a larger study. Results showed that the relationship between boredom and depression was strongest in moderate-to-severe TBI patients. We explored two boredom proneness factors that index an individual’s need for external or internal stimulation. Results indicated that the need for external stimulation was the critical driver in the relation between boredom and depression. Once again, this relationship was strongest in the moderate-to-severe TBI group. These results suggest that one common factor underlying boredom and depression is the need for stimulation from the external environment and, presumably, a failure to satisfy that need—a disconnection felt most strongly in moderate-to-severe TBI.