Necrosis is the consequence of ischemia. It entails insensitivity to all modes, followed by the formation of black and devitalized skin which gradually becomes lined and separated from healthy adjacent skin (by an eliminating groove), in a matter of days. Until proven otherwise, necrosis must always be treated as a medical or surgical emergency. Diagnosis of necrosis at the stage of black necrotic plaque comes too late. Early diagnosis is not always simple and requires experience. The following signs should be noticed: a painless part within a painful area, a pallor or drop in skin temperature within an erythematous area, and particularly a purpura with dark coloration. A needle can be used (SC or IM) to prick the suspected areas. In the absence of neuropathy, painlessness indicates a serious situation. The removal of the needle induces bleeding. If not, the necrosis is evolutive. It is therefore imperative to determine its cause, and appropriate treatment must be implemented without delay. The onset of necrosis can either reflect the severity of a cutaneous disorder (e.g., infectious cellulitis) or represent the cutaneous manifestation of a serious systemic disease (such as DIC, calciphylaxis).