A case of lethal invasive mucormycosis (IM), a rare fungal infection which predominantly affects immunocompromised patients, is reported in a 73-year-old female patient who presented with a cervical abscess. The patient had asthma treated with steroids and had previously undiagnosed diabetes mellitus. Despite surgical treatment and parenteral antibiotic therapy, there was fatal progression of the condition. The pathogenesis, histological appearances and treatment of mucormycosis are discussed, particularly the importance of urgent histological examination of debrided tissue to distinguish this condition from necrotizing fasciitis (NF) earlier than microbiological culture alone would allow, thus permitting the early introduction of appropriate antifungal therapy.