Pyoderma gangrenosum is an uncommon, ulcerative cutaneous condition of uncertain etiology (cause). It is associated with systemic autoimmune related diseases in at least 50% of patients who are affected. The diagnosis is made by excluding other causes of similar-appearing cutaneous ulcerations, including infection, malignancy, vasculitis, collagen vascular diseases, diabetes, and trauma. In a process termed pathergy, new ulcerations may occur after trauma or injury to the skin in 30% of patients who already have pyoderma gangrenosum. The prognosis of pyoderma gangrenosum is generally good; however, the disease may recur, and residual scarring is common. Pain is a common complaint of patients and may require narcotics.