Infection, trauma, and injury result in a stereotypical response that includes loss of food appetite, increased sleepiness, muscle aches, and fever. For thousands of years fever was considered a protective response, and fevers were induced by physicians to combat certain infections. But with the advent of antipyretic drugs, physicians started to reduce fevers, and fever therapy was virtually abandoned. As a result of (1) studies on the evolution of fever, (2) further understanding of just how tightly the process of fever is regulated, and (3) detailed studies on how fever affects host morbidity and mortality, the view of fever as a host defense response has reemerged. However, data indicate that not all fevers are protective and that high fevers are maladaptive. These issues are discussed in the context of the evolution of host defense responses versus modern medical technology. In short, we speculate that patients who would not have survived severe sepsis in the past are now being kept alive and that the occasionally high fevers seen in these patients may be maladaptive.