This paper describes the pilot phase of the National Traumatic Coma Data Bank, a cooperative effort of six clinical head-injury centers in the United States. Data were collected on 581 hospitalized patients with severe non-penetrating traumatic head injury. Severe head injury was defined on the basis of a Glasgow Coma Scale (GCS) score of 8 or less following nonsurgical resuscitation or deterioration to a GCS score of 8 or less within 48 hours after head injury. A common data collection protocol, definitions, and data collection instruments were developed and put into use by all centers commencing in June, 1979. Extensive information was collected on pre-hospital, emergency room, intensive care, and recovery phases of patient care. Data were obtained on all patients from the time of injury until the end of the pilot study. The pilot phase of the Data Bank provides data germane to questions of interest to neurosurgeons and to the lay public. Questions are as diverse as: what is the prognosis of severe brain injury; what is the impact of emergency care; and what is the role of rehabilitation in the recovery of the severely head-injured patient?