HEAD INJURIES CAN RESULT WHEN A STATIONARY HEAD IS STRUCK FROM WITHOUT BY A LARGE, BLUNT OBJECT, BUT THE MAJORITY OF BRAIN INJURIES OCCUR WHEN A MOVING HEAD STRIKES A STATIONARY OBJECT. DIAGRAMS SHOW THE TYPES OF INJURY MOST LIKELY TO RESULT WHEN A PERSON IS STRUCK ON THE CHIN, THROWING HIS HEAD BACK, WHEN ROTATION OF THE HEAD OCCURS AS PART OF THE FALL, AND WHEN THE HEAD IMPACTS AGAINST A STATIONARY OBJECT WITH STRAIGHT FORCE. BRAIN INJURY RESULTS FROM COMPRESSION OR PUSHING OF THE TISSUES TOGETHER, TENSION OR PULLING OF THE TISSUES APART FROM ONE ANOTHER, AND SHEAR OR SLIDING OF ONE PORTION OF TISSUE OVER ANOTHER. THE EFFECTS OF CONCUSSION, BRAIN SWELLING, INTRACRANIAL HEMORRHAGE. CONTUSIONS, LACERATIONS, AND BRAIN STEM LESIONS ARE DESCRIBED. THE SECTION ON HEMORRHAGE COVERS EXTRADURAL HEMORRHAGE, SUBDURAL HEMORRHAGE, SUBARACHNOID HEMORRHAGE, AND CEREBRAL CONTUSIONS AND LACERATIONS. BOTH MICROSCOPIC AND HISTOLOGICAL EXAMINATION ARE NEEDED TO ASSESS THE FULL EXTENT OF BRAIN DAMAGE. SEVERE PRIMARY HEAD DAMAGE IS USUALLY FATAL WITHIN HOURS OR DAYS. HOWEVER, MANY PEOPLE DIE FROM PREVENTABLE SECONDARY EFFECTS SUCH AS CLOTS OR INFECTIONS. TECHNIQUES FOR DIAGNOSING THE EXACT SITE OF INJURY, FOR DETERMINING LIKELY COMPLICATIONS, AND FOR ASSESSING EXTENT OF INJURY ARE DISCUSSED. THE ARTICLE IS WELL ILLUSTRATED WITH PHOTOGRAPHS. REFERENCES ARE APPENDED. (GLR)