Acute cutaneous necrosis is defined as a sudden onset of gangrenous skin changes in the skin, associated with significant morbidity and mortality. The following diseases are included in this discussion: coumadin necrosis, heparin necrosis, brown recluse spider bite, necrotizing fasciitis, vasculitis, pyoderma gangrenosum, calciphylaxis, clotting abnormalities and embolic phenomena. The importance of early diagnosis, early distinction and early drug therapy or drug withdrawal must match the diagnosis for maximal preservation of the skin and underlying tissue.