Nathan Zasler is CEO and Medical Director of the Concussion Care Centre of Virginia as well as Tree of Life Services, Inc., a living assistance and transitional neurorehabilitation program for persons with acquired brain injury in Richmond, Virginia. He is board certified in Physical Medicine and Rehabilitation, fellowship trained in brain injury and subspecialty certified in Brain Injury Medicine. He has lectured and written extensively on neurorehabilitation issues related to acquired brain injury. He has won numerous awards for his work in traumatic brain injury research, clinical care, and advocacy. Along with serving as chief editor of the international scientific publications, “Brain Injury” and “NeuroRehabilitation,” he also has edited seven books and currently serves as a reviewer for over 10 peer-reviewed scientific journals. Dr. Zasler is an affiliate professor in the Department of Physical Medicine and Rehabilitation at Virginia Commonwealth University in Richmond, Virginia, and associate professor, adjunct, in the Department of Physical Medicine and Rehabilitation at the University of Virginia. Dr. Zasler also is a fellow of the International Academy of Independent Medical Evaluators, as well as the American Congress of Rehabilitation Medicine and a diplomate of the Academy of Integrative Pain Management. In Part 1 of this two-part interview, Dr. Zasler discusses the following topics: time of onset of headaches following concussion and other more severe traumatic brain injury; the term “post-traumatic headache” as a diagnosis; factors that may influence the severity, frequency or aggravation of posttraumatic headaches; the degree to which preexisting conditions such as migraine and other conditions influence the likelihood that someone will suffer from posttraumatic headaches; whether screening should occur to determine the existence of sleep bruxism; other sleep disorders that may occur post concussion or TBI that clinicians should think about in the context of posttraumatic headache differential diagnosis; and factors important for clinicians to consider in the context of differential diagnosis of posttraumatic headache.