Fusobacterium necrophorum is a member of the normal flora of man that, unlike other commensal anaerobic non-spore-forming bacteria, can become a primary invasive pathogen causing serious and even life-threatening disease. It occurs primarily in previously healthy young people but the factors that trigger the invasive process are not understood. Systemic infections due to F. necrophorum have been described as Lemierre's disease, postanginal sepsis or necrobacillosis and in the context of this review, all are included under the umbrella term of 'invasive F. necrophorum disease' (IFND). Although IFND infections have been well documented for over a century, modern-day clinicians of various medical disciplines are often unaware of this syndrome and the severity of symptoms that it can cause. There are many descriptions of IFND disease in the literature and it is commonly referred to as a 'forgotten' disease. However, it is probably best described as a repeatedly 'discovered' disease, as it is uncommon and not mentioned in most major medical textbooks. There is some evidence that IFND is increasing particularly in the UK. The potential reasons for this are considered as part of a historical review, an update on disease incidence, patient demography, disease pathogenesis and laboratory diagnosis.