A new case of Campylobacter hyointestinalis-associated diarrhea in a human is reported. The medical history of the patient was significant for immunodeficiency because of an evolutive chronic myeloid leukemia. The diarrhea rapidly stopped after administration of oral erythromycin. No other enteropathogenic agent was found by routine examination of stools. Although neither serology nor autopsy was available, this observation appears to be suggestive of the possible enteropathogenicity of C. hyointestinalis for patients at risk.