Pyoderma gangrenosum is a clinical diagnosis. The ulcer shows three absolutely distinctive morphologic features: a purple-red, raised, undermined border; an irregular base, and cribriform scarring at the periphery. Evaluation of a patient with pyoderma gangrenosum requires a systematic search for possible associated inflammatory bowel disease or other internal disease. Although a variety of local treatments are used, systemic steroids are almost always necessary.