Between 1978 and 1980, 45 cases of acute monoblastic leukaemia have been diagnosed, treated and followed in our institute. Morphological diagnosis was performed according to the French-American-British classification. Tumoral syndrome (particularly extra-medullary) and hyperleucocytosis were the most striking findings at the time of diagnosis. Cytogenetic analysis performed in 31 cases before treatment has showed that abnormality of the long arm of chromosome 11 seemed to be more frequently associated with the poorly differentiated cytological subtype M5 (a). Intensive chemotherapy with zorubicin and cytosine arabinoside led to complete remission in 75% of the cases. Central nervous system prophylaxis appeared definitively useful in preventing meningeal relapse. Despite a prolongation of the median duration of complete remission which now reaches 12 months, the prognostic is still poor.