Necrotizing fasciitis is a severe soft tissue infection, often life-threatening, characterized by necrosis of the subcutaneous and fascial tissue, which can be extended along the fascial plans, affecting the adjacent vessels, nerves and muscle tissue. The predisposing factors of the disease include: advanced age, immuno-compromised bodies, diabetes, chronic alcoholism and chronic smoking. Necrotizing fasciitis in head and neck segments is rare, usually with an odontogenic source of infection. In the early stages of evolution, a necrotizing fasciitis is difficult to differentiate from the non-necrotizing infection of the soft tissue. Due to its extremely severe evolution, an early presumptive diagnosis is necessary (based on clinical and imaging aspects), as well as a prompt aggressive surgery backed by an intensive care support. The clinical case of an immunocompromised patient admitted for a mouth floor diffuse suppuration, previously complicated with cervicothoracic necrotizing fasciitis with aggressive evolution, is discussed in the following.