Skin thickening and subcutaneous air were detected at ultrasound (US) of the scrotum in a patient with normal-appearing testicles and signs and symptoms suggestive of an acute inflammatory process, such as epidydimitis or orchitis. The patient was found to have Fournier gangrene. In more advanced cases, US can demonstrate that this skin thickening and subcutaneous air extends posteriorly to include the perineum and buttocks. Because of the high mortality of this mixed anaerobic and aerobic infection, it is important to recognize Fournier gangrene early so that the correct surgical and medical treatment can be promptly instituted. To the authors' knowledge, this is the first description of the US characteristics of Fournier gangrene.