This retrospective epidemiologic study on 256 cases of Acute Promyelocytic Leukemia (APL) observed in 20 Italian hematology centers between 1980 and 1988 demonstrated that APL is different from the other acute non-lymphocytic leukemias (ANLL). The male/female ratio was 0.9; median age at diagnosis was 40 years (with 80% of patients between 15 and 54 years of age). The minimal annual incidence of APL in Italy per 1,000,000 inhabitants was estimated to be 0.6; an increased incidence was observed in spring and in autumn. The overall median survival duration of APL patients was 12.6 months. From an epidemiological point of view APL is a distinctive subtype of ANLL.