Pyoderma gangrenosum (PG) is a necrotizing and ulcerative skin disease of unknown cause. The pathogenesis is thought to be related to a defective immune response. The ulcerations appear spontaneously or after skin trauma. Development in a surgical wound can be misinterpreted as wound infection. However, in contrast to postoperative infections, treatment of PG requires immunosuppressive therapy. We report a case of PG following hip-joint surgery that was complicated by a severe life-threatening systemic inflammatory response syndrome (SIRS). Typically, wound and blood cultures were negative for pathogens. Prednisolone stopped the activity of the disease promptly.