Acute promyelocytic leukaemia (A.P.L.) is a rare but important type of acute myeloid leukaemia characterized by major bleeding in association with thrombocytopenia, a specific peripheral blood and bone marrow picture, low plasma fibrinogen, and the presence in the serum of fibrin degradation products. These last abnormalities are related to the disseminated intravascular consumption of coagulation factors with secondary fibrinolysis. A.P.L. requires early recognition and urgent treatment. With optimal management up to half of the patients may achieve complete remission of two years or more. Undoubtedly patients with A.P.L. do especially well when treated in special centres and some patients with A.P.L. now die before the nature of their disease is recognized. Increased familiarity with the problem, which has been known for nearly 20 years, should yield great dividends for those few patients who have this disease.