Traumatic neurologic injuries, such as spinal cord injury (SCI) and traumatic brain injury (TBI), cause long-term disability. “Dual diagnosis” refers to concurrent diagnosis of SCI and TBI following traumatic injury. Rate of dual diagnosis has been increasing in the United States, accounting for 2.46 per 100,000 admissions in 2008. As with isolated SCI and TBI, dual diagnosis more frequently occurs in men and following motor vehicle collisions. At this time, there are only limited data on the pathophysiology, medical complications, and outcomes of patients with dual diagnosis. In this review article, we will discuss the epidemiology, pathophysiology, and functional outcomes after dual diagnosis injury. We will also summarize the clinical presentation and management of common medical complications arising from injury, such as spasticity, dysautonomias (autonomic dysfunction in SCI and paroxysmal sympathetic hyperactivity in TBI), heterotopic ossification, and neuroendocrine dysfunction. It is important to understand the role that dual diagnosis plays in the rehabilitation course and long-term outcomes in order to implement a tailored rehabilitation program.