Summary: Postoperative pyoderma gangrenosum is a rare neutrophilic dermatosis that may be confused for necrotizing fasciitis. The inflammatory response is triggered by the trauma of surgery and thus must be managed nonsurgically. Clinical and pathological findings in the 2 diseases can be identical, leading to misdiagnosis and massive surgical defects from the ensuing surgery. This report documents a severe case of postsurgical pyoderma following an elective rotator cuff repair presenting with myositis and myonecrosis. The patient was initially treated as having an infection, which resulted in multiple aggressive surgical debridements. Despite this, the patient continued to deteriorate and was in a critical and hemodynamically unstable condition. Following administration of high-dose intravenous corticosteroids, the patient made a dramatic recovery and went on to have internal fixation of the shoulder and closure of the wound with a combination of a free flap and a rotational flap. Extensive myositis, as seen in this case, has not been previously reported in postoperative pyoderma gangrenosum variants. Clinicians should be aware that the presence of myositis and myonecrosis should not preclude this diagnosis.