urrently, respiratory diseases account for 25-30 per cent of the total infectious and parasitic disease admissions among active duty Navy and Marine Corps (henceforth naval) personnel. Among these admissions, the greatest medical cause of lost workdays is pneumonia, due both to its frequency of diagnosis and to the relatively long hospitalization period associated with this disease. Because of the diversity of pathogens associated with the pneumonia syndrome, pertinent epidemiological information is difficult to extract from clinical observation or health surveys, except in the most general sense. A closed system of health care, such as that provided by the Navy, offers an opportunity to evaluate the significance of this disease in terms of its epidemiology, and to identify new areas for research which will further our understanding of factors contributing to patterns of pneumonia occurrence. The data available for study were hospital admission records of active duty naval personnel with primary diagnoses of pneumonia. By calculating and comparing specific admission rates for pneumonia, we identified high risk groups within the population and the temporal trends associated with morbidity. Methods The admission records included all active duty Navy and Marine Corps patients for whom inpatient care was carried to completion at a naval medical treatment facility, or who were discharged from the facility without intent of transfer for continued inpatient care at another Armed Forces facility. Pneumonia admissions were categorized according to the Eighth Revision International Classification of Diseases Adapted for Use in the United States (ICDA-8). The period of study for age, race, and sex adjusted admission rates was 1974-1978, and 1970-1979 for unadjusted rates. The data base for this project was established from information retrievals done with the computer system files of the NMDSC. Admission records were retrieved for specific diagnoses along with the selected variables of race, sex, age at admission, and branch of Service. Overall annual admissions rates by disease category, and selected age, race, and sex specific rates were computed. When appropriate, admission rates were ad-From the