Abstract
A previously healthy 74-year-old Japanese female was hospitalized with fever and high C-reactive protein. She developed palatal herpangina-like aphthous ulcers, localized intestinal wall thickening, terminal ileum ulcers, and an erythematous acneiform rash; thus Behçet's disease-like illness was suspected. Significant peripheral blood acute monocytosis developed during her hospitalization and acute monocytic leukemia (FAB M5b) with normal karyotype was diagnosed. By immunostaining, the infiltrating cells in the skin and the terminal ileum were identified as monocytic leukemic cells. This case exhibited a unique initial presentation of Behçet's disease-like illness associated with acute monocytic leukemia.