With the increased prevalence of human immunodeficiency virus and acquired immunodeficiency syndrome in children and adolescents, diagnosis and treatment of other associated diseases, many of which pose specific risks for this particularly vulnerable population, are of concern to pediatricians. An important opportunistic infection associated with this increased prevalence is Pneumocystis carinii pneumonia, which recently has occurred in epidemic proportions in these populations. Untreated, the disease always is fatal. Since his first descriptive report on P carinii pneumonia in 1971, Walter T. Hughes, MD, has been the unequaled authority on the disease, its prevention, and its treatment. He is the subject of this article, which seeks to honor his outstanding research accomplishments, his commitment to his profession and to his patients, and his devotion to his family, all of which find their source in his faith. Copyright © 2001 by W.B. Saunders Company