Retroperitoneal abscesses are unusual occurrences with occult and insidious presentations. There is often a lack of abdominal signs, leading to delays in drainage and high mortality rates. We report a case of thigh emphysema in an 88-year-old patient with diabetes. Prior to admission the patient reported a vague 4-week history of left thigh pain and an inability to fully weight bear. She presented to our emergency department with sepsis and acute kidney impairment. An X-ray of her left femur revealed widespread gas between muscular planes. A retroperitoneal abscess involving the left renal fossa, psoas, iliacus and upper thigh muscles was revealed on an urgent CT scan. The patient was transferred to intensive care unit (ICU) and underwent an emergency drainage. Despite ICU the patient died 2 days after admission.