ObjectiveTo improve the understanding of chronic myelomonocytic leukemia associated with Sweet' s syndrome.MethodsRetrospective analysis of a case of chronic myelomonocytic leukemia associated with skin herpes was reported. Skin biopsy was performed. DA and CAG regiment were administrated.ResultsSweet's syndrome was diagnosed by skin biopsy.Corticosteroids therapy alone was not effective. Complete remission was achieved by CAG regiment and skin rash has been effectively controlled.Three months later Sweet' s syndrome relapsed and chronic myelomonocytic leukemia developed into acute myelomonocytic leukemia. ConclusionChronic myelomonocytic leukemia associated with Sweet's syndrome is rare but implies a quick progression to acute myelomonocytic leukemia.