To describe secular trends in pneumonia hospitalizations in the Bronx, New York City from 1982-1986, we analysed all cases with a discharge diagnosis of pneumonia, excluding Pneumocystis carinii pneumonia (PCP), for Bronx residents by age, sex, neighbourhood, and length of stay (N = 21,822). Hospital deaths from PCP and immune disorders were analysed separately as a non-recurrent indicator of human immunodeficiency virus (HIV) related disease prevalence by age, sex and geographical areas. From 1982 to 1986, pneumonia hospitalizations increased 132% among males and 100% among females aged 25-54, an age group accounting for 90% of adult AIDS cases in the Bronx, as compared to a 21% rise among males and 38% among females in all other age groups (p less than 0.001). Pneumonia rates increased most in those population groups with the highest rates of PCP and immune disorders. An ecological correlation of pneumonia hospitalization with this measure of AIDS prevalence for residents of a small geographical area is evident (r2 = 0.92). The observed increase in pneumonia hospitalizations, believed to be related to underlying prevalence patterns of HIV in this population, accounts for a significant and previously unrecognized burden on the local health care system. From 1983-1986, these 'excess' pneumonias in the Bronx accounted for 14,707 days of hospitalization--equal to 42% of the total days attributed to all hospital admissions for AIDS per se.