A territory-wide prevalence survey of hospital infection in 10 Hong Kong hospitals was carried out in January 1987 using a standard protocol. Out of 9848 patients included in the survey, 2542 (25.8%) had infection, of which 844 (8.6%) were acquired in hospital and 1746 (17.7%) in the community. Although in North American studies there are higher rates of hospital-acquired infection in tertiary-referral and university-affiliated hospitals than in community hospitals, this was not found to be the case in Hong Kong. Factors contributing to the high rate of hospital-acquired infection in Hong Kong include the proportion of high-risk patients, the frequency of inter-hospital transfers, the crowdedness of wards and the education level of staff. In Hong Kong, hospital-acquired infections are important in large, as well as in small, hospitals.