Within the 3-y period 1992-94 a total of 815 episodes of monomicrobial bacteraemia caused by Enterobacteriaceae not including Salmonella were registered in the County of Northern Jutland. The 30-d case fatality rate was 24%, ranging from 21% for Enterobacter spp. (n = 43), 22% for E. coli (n = 577) to 32% for both Klebsiella spp. (n = 138) and a group of miscellaneous enterobacteria (n = 57). In 16% of the bacteraemias, antibiotic treatment was not instituted before notification of positive blood cultures; in 9% empirical antibiotic treatment was inappropriate. Antibiotic regimens mainly included beta-lactams, ampicillin or mecillinam in combination with an aminoglycoside. The following factors were independently associated with case fatality: age > or = 75 y, high comorbidity index, admission to a medical ward or an intensive care unit, nosocomial acquisition, a source of infection outside the urinary tract or an undetermined focus, Klebsiella spp., inappropriate coverage or lack of antibiotic treatment before notification of positive blood culture. It is a matter of concern that in one-sixth of patients the physicians had not responded to the possibility of bacteraemia with institution of empirical antibiotic therapy.