The white-cell count acquires an important prognostic value in acute leukaemia. Thus, very high leucocytosis conveys high risk of early death due to leucostasis. The clinico-biological features at diagnosis, response to therapy and prognostic factors of 69 cases of acute leukaemia with hyperleucocytosis (ALHL) are reported in this paper. All the patients had white-cell count over 100 x 10(9)/L and had been followed up at the Haematology Service of the Hospital La Fe between 1977 and 1989. There were 49 cases of acute nonlymphoblastic leukaemia (ANLL), 18 cases of acute lymphoblastic leukaemia (ALL) and 2 of unclassified acute leukaemia. The incidence of ALHL was 14%, and the mortality on the first week after diagnosis reached 20%, this being higher in ANLL. The actuarial median of complete remission duration was 9 months. The achievement of remission was associated with the morphological subtype, the patient's age and the presence of constitutional symptoms at onset, while the duration of remission was associated with the presence of fever and the need more than one chemotherapy course to attain remission. ALHL need new therapeutic strategies in order to diminish the rate of early death and to achieve longer survival.