Tension pneumocephalus is a rare neurosurgical emergency requiring cranial decompression to prevent permanent neurological injury, herniation, and death. In this report, we present a trauma patient struck by a knife in the forehead who presented with agitation and vomiting. Imaging ultimately revealed a minimally displaced frontal sinus fracture through both the anterior and posterior walls of the sinus. This disruption, acting as a ball-valve for air entry into the cranium, resulted in extensive pneumocephalus and eventual tension physiology. The patient required immediate neurosurgical decompression. This case illustrates both the importance in recognition of this uncommon pathology as well as the need for rapid reassessment with clinical changes in trauma patients.TopicsTension pneumocephalus, facial fracture, head trauma.