The first national survey of the prevalence of nosocomial and community-acquired infections in Australian hospitals was carried out during July 1984. Data were collected on 28,643 patients in rural and metropolitan, public and private acute-care hospitals. The over-all adjusted prevalence of nosocomial infections was 6.3%; the prevalence of community-acquired infection was 9.7%. A total of 5940 infections occurred; 39% were hospital-acquired infections and 61% were community-acquired infections. These occurred at the following sites: the respiratory tract, 35.4% (2100 infections; contributing 19% of hospital-acquired infections and 46% of community-acquired infections); the urinary tract, 15.1% (896 infections; contributing 22% of hospital-acquired infections and 11% of community-acquired infections); surgical wounds, 13.4% (797 infections; contributing 34% of hospital-acquired infections); the gastrointestinal tract, 7.8% (466 infections; contributing 3.4% of hospital-acquired infections and 11% of community-acquired infections); skin, 6.3% (376 infections; contributing 4.4% of hospital-acquired infections and 8% of community-acquired infections); abscesses, 1.9% (113 infections; contributing 0.9% of hospital-acquired infections and 2% of community-acquired infections); traumatic wounds, 1.5% (90 infections; contributing 0.9% of hospital-acquired infections and 2% of community-acquired infections); bacteraemia, 1.5% (89 infections; contributing 1.6% of hospital-acquired infections and 1% of community-acquired infections); burns, 0.2% (14 infections; contributing 0.3% of hospital-acquired infections and 0.2% of community-acquired infections); and other, 16.8% (999 infections; contributing 13.4% of hospital-acquired infections and 19% of community-acquired infections). There was a significant association between hospital size and infection rates. The nosocomial infection prevalence rate increased from 4.2% in hospitals with 50-99 beds to 7.6% in hospitals with 500 or more beds. The prevalence of community-acquired infections was higher in rural (11.5%) than in metropolitan (8.7%) hospitals. After adjusting for hospital size, public hospitals had significantly-higher prevalences of nosocomial (6.7%) and community-acquired (10.6%) infection than did private hospitals (nosocomial infection, 4.8%; community-acquired infection, 6.3%).