The WHO classification moved CMML to myeloproliferative/myelodysplastic disorders, and defined CMML I and CMML II according to medullary and peripheral blast count. To confirm these proposals, we analyzed 266 patients with CMML I and 73 patients with CMML II. Median survival time was 20 months for CMML I, and 15 months for CMML II (p<0.005). The cumulative risk of AML evolution differed between patient groups (p=0,001). No conclusive differences in clinical, morphologic, hematologic or cytogenetic parameters were found. These data support the WHO proposals for the classifi-cation of CMML.