Hyperleukocytic acute myeloid leukaemia is considered to have a poor prognosis due to high early death rate secondary to leukostasis. Supportive treatments do not seem to have reduced early exitus in this subset of patients. Prognostic impact of hyperleukocytosis on outcome has been the object of few studies. Clinical characteristics and outcome of 45 consecutive adult patients with newly diagnosed acute myeloid leukaemia presenting to our institution with a white cell count (WBC) above 100 x 10(9)L(-1) were reviewed. The outcome of this subset of patients was compared with 200 patients with a leukocyte count lower than 100 x 10(9)L(-1) similarly treated in the same period. Eight hyperleukocytic patients (17%) died of intracranial haemorrhage or pulmonary failure due to leukostasis within the first 7 days of treatment. A significant association was found between complete response (CR) and absence of hyperleukocytosis, but if early deaths were removed from analysis the difference was no longer significant. Hyperleukocytosis also significantly reduces the overall survival (OS) but does not significantly influence the disease-free survival (DFS). We reviewed in literature studies in which the outcome of series of at least 10 patients with hyperleukocytosis were compared with that of patients with a leukocyte count lower than 100 x 10(9)L(-1). Our data were consistent with those of the literature regarding the rate of early mortality and causes of death. In most of the reviewed series hyperleukocytosis does not seem to influence the outcome of patients. Avoiding early death seems to be an important step in this subset of patients. New data about pathophysiology of leukostasis are needed.