The article discusses the Lemierre's syndrome or necrobacillosis, a fatal systemic anaerobic bacterial infection associated with Fusobacterium necrophorum. A case of a 14-year-old girl with Lemierre's syndrome and was admitted to hospital 10 days after a throat infection is being discussed. The patient has been treated initially with erythromycin, an antibiotic unsuitable for fusobacterial infections, because of allergies to penicillin. The right descriptions of true penicillin allergy coupled with the patient's description of what they believe to be allergic responses is also discussed.