Pulmonary dysfunction is a common complication of severe head injury. The degree of initial hypoxemia which develops appears to correspond with the location and magnitude of the head injury. If unrecognized and not aggressively treated, the hypoxic insult will magnify the cerebral insult. A severe postinjury hypermetabolic state also develops and, if unrecognized and not managed aggressively with nutritional support, can also lead to severe catabolism, increased infection, and further lung dysfunction. Although supportive care is the major treatment at present, pharmacologic manipulation of the increased catecholamine activity, which is considered to be causative, may be effective in controlling both the impaired gas exchange and the hypermetabolic state. A knowledge of the various lung dysfunction states which occur in the head-injured patient population is required to optimize recovery and minimize complications.