There is an ever increasing population of patients who merit the designation ‘compromised host’. They fall into two separate categories, one a disaster, the other a triumph. The disaster is, of course, the HIV/AIDS epidemic which has resulted in an epidemic of opportunistic infection around the world. However, since the summer of 1981, when AIDS was first recognized, remarkable progress has been made - the etiology and pathogenesis of AIDS have been established; diagnosis and prognosis (viral load and CD4-positive lymphocyte counts) have been defined; and HAART (Highly Active Anti-Retroviral Therapy) therapy has become the standard of care. Despite drug toxicities and interactiions, despite high costs, and despite problems with drug resistance, HAART therapy has made a major difference in the lives of those infected with HIV. At the same time, AIDS in its many forms is no longer a conditiion relegated to ivory towers and academicians. It is now the province of all practitioners, and the requirements for expertise are the province of primary care physicians as well as academicians. The triumph is a result of the great success being achieved in the care of cancer patients, transplant recipients, autoimmune diseases, and the expert use of immunosuppressive drugs for many conditions. The underlying diseases of these patients are, for the first time in history, being controlled, and are no longer the major determinant of morbidity and mortality. The great paradox is that the major threat to these patients is no longer the underlying disease, but rather it is the infections that are engendered by the life saving therapy. New paradigms of management are necessary, and it is useful to think in terms of the therapeutic prescription, which has two components: an immunomodulating component to control the underlying disease, and an antimicrobial component to make it safe. The authors of the individual chapters of the 5th edition uniformly can be regarded as leaders in this field. They will scientific rigor, clinical wisdom, and the generous use of case examples to this next edition. The Compromised Host remains a worthy target, and the insights to be gained are both important and remarkable. Note: The 2nd and 3rd editions of this work received the Certificate of Commendation from the British Medical Association Medical Book Competition in 1989 and 1995 respectively.