During a period of 10 years, 293 of 4270 admissions to the general intensive care unit (ICU) at Medway Maritime Hospital had 356 bacteraemias due to one of 14 microorganisms. Incidence of bacteraemia was least on the third day after admission, significantly greater on the fifth day and stable thereafter. From the fifth day the acquisition rate was 18.9 (16.5-21.3)/1000 bed-days, lower in those with an initial Acute Physiological Assessment and Chronic Health Evaluation II score (APII)18, or admitted from the emergency room. A total of 1395 patients with no positive cultures in the first four days stayed in ICU foror=5 days, and 204 subsequently had one or more bacteraemias. Hospital mortality in these patients was 45.6% (38.8-52.4), greater than in those with similar APII but sterile cultures [relative risk (RR): 1.30 (1.04-1.63) and matched controls, RR: 1.33 (1.09-1.63)]. Observed mortality was greater than predicted only in bacteraemic patients [RR: 1.31 (1.03-1.67)]. ICU-acquired bacteraemia was associated with an approximate additional absolute mortality of 11% contributing 0.5% to the 29.9% hospital mortality of all ICU admissions, 1.6% to the 34.6% of those stayingor=5 days, and 5.6% to the 35.9% of those remaining24 days.