The differential diagnosis of patients with ulcerative trachelophyma repeatedly causes difficulties. Particularly in view of the possibly fatal outcome, early differentiation between two clinical pictures is very important. Necrotizing fasciitis is often misdiagnosed or the diagnosis is delayed with a mortality rate of approximately 25-40%. It is characterized by local disintegration of the subcutaneous fascia and extensive gangrene of the skin. Sometimes it is not even possible to control the disease using combined antibiotics. Early surgical exploration is mandatory to stop progression of the disease. Pyoderma gangrenosum develops following an initial lesion with pustules and bullae in an ulceration with slight bleeding. Therapy consists of i.v. glucocorticoids (60-200 mg prednisolone/day) administered as early as possible. In complete contrast to the therapy for necrotizing fasciitis, surgical intervention should be strictly avoided in cases of pyoderma gangrenosum.