The genus Campylobacter includes gram-negative, motile, curved rods that can evidence characteristic morphologies. These microorganisms require low oxygen tension and an increased level of CO2 for growing. A case of bacteremia due to Campylobacter fetus in a patient with a previous diagnosis of breast cancer with metastases in dorso-lumbar column and acute promyelocytic leukemia (FAB-M3 variant) is presented. The patient was admitted to our institution due to loss of consciousness and a 2 day--history of bloody diarrhea. She received successive blood transfusions on account of her pancytopenia. Thirteen days later she developed high-grade fever. Samples were taken for blood and urine cultures and antibiotic treatment with clindamycin and ciprofloxacin was instituted. Blood culture bottles were subcultivated at 48 hours in chocolate agar. After 24 hours of incubation at 35 degrees C in a 5% CO2 atmosphere (candle jars), tiny colonies developed. Gram stain showed spiral-shaped gram-negative rods in both samples. The strain was identified as Campylobacter fetus by conventional biochemical tests. The antibiotic therapy was switched to clindamycin and gentamicin. The patient evolved favorably with negative blood cultures after a 5 day- treatment.