The combined cause-of-death category pneumonia and influenza (P&I) (International Classification of Diseases, Ninth Revision, codes 480-487) ranks as the sixth leading cause of death in the United States following heart disease, cancer, stroke, unintentional injuries, and chronic obstructive pulmonary disease. Changes in the epidemiology of Streptococcus pneumoniae and other recognized respiratory pathogens, the increasing occurrence of drug-resistant microorganisms, and the detection of new respiratory pathogens have heightened awareness of the public health importance of severe respiratory infections. To characterize the epidemiology of P&I deaths in the United States, CDC further analyzed underlying and multiple cause-of-death mortality files for 1979-1994. This report summarizes the results of this analysis.