Hospital acquired infections (HAI) continue to constitute a major health problem for hospital patients. Such a problem is particularly relevant in Intensive Care Wards. Here infections appear to be directly or indirectly related to the patients' death, and the patients, of course, represent a selected group of the most susceptible hosts in the whole hospital due to their immunosuppressed states, underlying diseases and the numerous and highly invasive diagnostic and therapeutic procedures to which they are submitted. This paper reports the results of a one-year surveillance incidence study carried out in four Intensive Care Wards at Padua Hospital by means of a daily visits to the wards and careful collection of the patients' data in a computerized sheet. Two-hundred-thirty-one of the 859 patients considered developed one or more HAI (HAI percentage 26.9%) for a total of 382 HAIs (Infections ratio 44.5%). Nosocomial pneumonias were the most frequent infections detected, whereas urinary tract infections, bacteremias and wound infections were less common in such patients. The study also confirmed the importance of invasive procedures and surgical operations in the predisposition to HAIs. In particular, the importance of the urinary catheter and of tracheal intubation was outlined. In addition, HAI appeared to be related to the duration of hospitalization and to the severity of the patients' illness. HAIs (especially nosocomial pneumonias) were also closely related to the patients' death. Pseudomonas aeruginosa, S. aureus, Acinetobacter and Streptococcus D were the most frequently isolated agents in the infected patients. Gram-negative agents accounted for 57% of all agents isolated and were particularly frequent in both pneumonias and urinary tract infections.(ABSTRACT TRUNCATED AT 250 WORDS)