Necrotizing soft tissue infections (NSTI) is a serious infection with a mortality of up to 25% at three months. This review gives an overview of the diagnosis and treatment of NSTI. The prognosis is dependent on rapid surgical treatment, aggressive, prompt removal of infected tissue, broad spectrum antibiotic treatment and supportive care. In cases with suspected or verified infection with Streptococcus pyogenes, adjuvant therapy with immunoglobulins can be considered.