A 47-year-old man presented to the hospital with a 2-day history of weakness and fever. His blood pressure was 64/47 mm Hg, heart rate 110 beats per minute, and temperature 39.0°C. On physical examination, the patient had swelling and redness of the left thigh, which aroused concern about the presence of an abscess. Laboratory studies showed pancytopenia and extreme elevation of the d-dimer level. Promyelocytic blast cells with intracellular Auer rods — needle-shaped cytoplasmic structures specific for myeloid neoplasms — were seen on a peripheral-blood smear. Owing to concern about acute promyelocytic leukemia and sepsis, the patient was admitted to the intensive care unit. Induction chemotherapy with all-trans retinoic acid and prednisolone was initiated. A bone marrow biopsy showed promyelocytes with abundant intracellular Auer rods in formations that resembled bundles of sticks (arrows). Genetic analysis for chromosomal translocation identified a PML–RARA fusion gene. A diagnosis of acute promyelocytic leukemia was confirmed. Two days after the start of treatment, differentiation syndrome developed. The hospital course was further complicated by the presence of disseminated intravascular coagulation and Staphylococcus aureus bacteremia with leg abscesses. After molecular complete remission had been attained, consolidation chemotherapy that included arsenic trioxide was administered. On hospital day 72, the patient was discharged.