Rat bite fever is a poorly recognised entity, characterised by a series of clinical manifestations in which fever and polyatrial involvement predominate.The unspecificity of the symptoms together with the difficulty in isolating the causative germ causes delays in diagnosis, so active questioning in search of previous contact with rats or rodents is the fundamental basis for early diagnosis and timely treatment of this entity.Delayed treatment can result in mortality in up to 10% of patients.