We encountered a 76-year-old woman with acute myelogenous leukemia (AML) who developed Sweet's syndrome. A biopsy specimen taken from her skin lesion on the upper arm showed an infiltration of numerous neutrophils intermingled with leukemic cells. As far as we know, this is the first report of Sweet's syndrome showing a phenotypically identified leukemic cell infiltration of AML determined as M2 in the French-American-British classification.