Chronic pain patients and brain injured patients frequently exhibit anxiety, depression, perseveration, and fixed ideation about their injuries. Both populations also frequently suffer from decreased attention, impaired concentration, easy fatigability, personality changes, impaired relationships with family and friends, and difficulty maintaining a job. In cases where chronic pain coexists with traumatic brain injury, the brain injury is often obscured. Risk factors which should alert the medical team to possible coexisting brain injury include history of loss of consciousness at original injury, history of trauma to the head, whiplash injury to the neck, multisystem trauma, and admission of memory or attention deficits by the patient. When any of these risk factors are present, we have found that formal examination of cognitive function is required to explore the potential of coexisting brain injury; if pain is a prominent clinical feature, residual cognitive sequelae of mild brain injury is easily masked. Specific testing of attention, new learning ability, constructional ability, and higher cognitive functions are most helpful in this population, and they need to be included in the mental status examination when concomitant brain injury is suspected. In our study, seven patients were found to have undiagnosed brain injury in a series of 67 consecutive patient referrals to our pain rehabilitation program. Treatment failure is high in this subgroup of pain patients unless treatment is directed toward the sequelae of both brain injury and chronic pain.