Lemierre's syndrome (or Lemierre's disease) is a disease caused by the bacterium Fusobacterium necrophorum, and usually affects young, healthy adults.

The first symptoms are just a sore throat, but after a couple of weeks this is followed by septicemia (infection of the blood) which can cause complications in other parts of the body including the lungs, liver and joints if untreated.

Lemierre's syndrome is easily treated with antibiotics, but because sore throats are most commonly caused by viruses, for which antibiotic treatment is unnecessary, such treatment is not usual in the first phase of the disease.

Lemierre's syndrome is currently a very rare disease, but was quite common in the early 20th century before the discovery of penicillin.