To determine the incidence and outcome of critical illness amongst the total population of hospital patients with haematological malignancy (including patients treated on the ward as well as those admitted to the intensive care unit), consecutive patients with haematological malignancy were prospectively studied. One hundred and one of the 1437 haemato-oncology admissions (7%) in 2001 were complicated by critical illness (26% of all new referrals). Fifty-four (53%) of these critically ill patients survived to leave hospital and 33 (34%) were still alive after 6 months. The majority (77/101) were not admitted to the intensive care unit but were managed on the ward, often with the assistance of the intensive care team. Independent risk factors for dying in hospital included hepatic failure (odds ratio 5.3, 95% confidence intervals 1.3-21.2) and central nervous system failure (odds ratio 14.5, 95% confidence intervals 1.7-120.5). No patient with four or more organ failures or a Simplified Acute Physiology Score II >/= 65 survived to leave hospital. There was close agreement between actual and predicted mortality with increasing Simplified Acute Physiology Score II for all patients, including those not admitted to intensive care.