This study examined the association between type of haematological malignancy, risk of bacteraemia and risk of mortality, with emphasis on the impact of bacteraemia type on mortality. A population-based cohort design was used, and all patients aged > or = 15 years with an incident haematological malignancy who were living in North Jutland County, Denmark, during 1992-2002 were included in the study. Among 1666 patients with an incident haematological malignancy, 358 (21%) suffered an episode of bacteraemia during a median follow-up period of 1.1 years (quartile 0.2-3.4) from the date of cancer diagnosis (overall incidence rate of 96/1000 person-years). In comparison to Hodgkin's disease, adjusted incidence rate ratios (IRRs) were 23.3 (95% CI, 10.0-54.5) for acute myeloid leukaemia, 3.8 (95% CI, 1.5-9.3) for multiple myeloma, and 2.2 (95% CI, 0.9-5.1) for non-Hodgkin's lymphoma or chronic lymphatic leukaemia. Overall cumulative 30-day mortality was 32% (95% CI, 27-37), and 90-day mortality was 50% (95% CI, 44-55). In comparison with acute myeloid leukaemia, adjusted mortality rate ratios (MRRs) were close to 1.0 for other haematological malignancies. In comparison to bacteraemia caused by Gram-positive bacteria, adjusted MRRs were 1.0 (95% CI, 0.6-1.5) for Gram-negative bacteraemia, and 1.9 (95% CI, 1.1-3.3) for polymicrobial bacteraemia or fungaemia. Thus, the risk of bacteraemia varied greatly according to the type of malignancy, while mortality rates were similar for these diseases, although dependent on the type of bacteraemia. Polymicrobial bacteraemia or fungaemia was associated with higher mortality.