A 1-day prevalence survey of hospital-acquired infections (HAI) was carried out in Norwegian somatic hospitals in 1991. The survey aimed at assessing the problem of HAI. 950 infections were found among the 14977 surveyed patients (prevalence rate 6.3%). HAI were more prevalent in combined intensive care units (prevalence rate 22%), surgical intensive care units (17%), haematological wards (15%), special care baby units (14%), and geriatric wards (14%). Urinary tract infections were most prevalent (33% of all HAI) followed by respiratory tract infections (21%) and surgical wound infections (17%). 157 (3.6%) of the 4382 patients who had undergone surgery, had a surgical wound infection. With a high response rate (76 out of 84 hospitals) and a sensitive method of screening the patients (chart review and bedside examination), this survey gives a fairly reliable measure of the prevalence of HAI in Norwegian somatic hospitals.