We present the case of a 75-year-old woman who presented with extensive breast cellulitis, which was thought to be secondary to a deep breast abscess. On admission the patient underwent debridement of the breast and broad-spectrum intravenous antibiotics were administered. However, during hospitalisation she developed sepsis, acute renal failure and required further debridements for the rapidly spreading necrotising fasciitis. Subsequently, a partial mastectomy was performed and the patient made an overall good postoperative recovery.