Introduction: Gas gangrene is a rare, often lethal infection of soft tissue that is commonly associated with the Clostridial species due to penetrating injuries. Case reports of spontaneous atraumatic gas gangrene due to the Clostridium septicum species are exceedingly rare. Atraumatic C. septicum is notably related to bowel pathologies, immunodeficiencies, and individuals with vascular insufficiency. The rapid progression of Clostridium myonecrosis contributes to its high mortality rates. Case Report: The authors report a case of a 71-year-old right-hand-dominant female who developed fulminant atraumatic left forearm pain and swelling. The patient was indicated for emergent irrigation and debridement (I&D) of the left upper extremity. She was later found to have C. septicum bacteremia and required multiple I&Ds including the left side of the neck and chest wall. Repeat post-operative examinations revealed no motor function or sensation distal to the elbow and she was subsequently indicated for a proximal trans-humeral amputation. Conclusion: Although she had a prolonged hospital stay, she progressed well and was eventually discharged to a rehabilitation facility. This case report highlights the importance of early recognition of Clostridial myonecrosis as well as the need for emergent surgical intervention for the patient’s survival. Keywords: Trans-humeral amputation, gas gangrene, Clostridium septicum infection.