Sunken Skin Flap Syndrome (or Syndrome of the Trephined) following a head trauma is rare, but most often results from complications after decompressive craniectomy. This syndrome is most often characterized by neurological dysfunction that improves with cranioplasty. Early diagnosis and treatment are critically important to long term neurological improvement. This is a case report of a 49-year-old male who fell down a flight of stairs and was found unresponsive. Initial imaging revealed extensive head trauma. Neurosurgery performed an emergency decompressive craniectomy, but his post-operative course was complicated by the development of sunken flap syndrome one month after his initial surgery, diagnosed by an acute neurological decline and emergent CT imaging. A review of the literature indicates that this is a rarely documented finding, and this case report discusses the critical components of diagnosis and treatment of this unusual and potentially lethal condition.