Background <p>Diabetes mellitus is a metabolic disease that serves as an independent risk factor for the development of various pathologies, including mucormycosis.</p> Case presentation <p>A 47-year-old male, citizen of the Russian Federation, when seeking medical assistance, presented with the following complaints: pain, swelling, and numbness of the right side of the face; difficulty in nasal breathing through the right nasal passage, with purulent nasal discharge; reduced visual acuity in the right eye; a feeling of shortness of breath; dyspnea at rest; and general weakness. Diabetes mellitus and ketoacidosis were diagnosed for the first time. A comprehensive study was conducted, including radiological imaging, laboratory, and microbiological diagnostics. A clinical diagnosis was made: mucormycosis, rhino-orbito-cerebral form (<i>Rhizopus oryzae</i>). The components of the patient’s treatment included surgical intervention with removal of nonviable tissues and etiotropic therapy. This clinical case ended in a fatal outcome.</p> Conclusion <p>Timely seeking of medical assistance, early diagnosis of the disease, prompt initiation of etiotropic therapy, and complete removal of affected tissues are key to the effectiveness of mucormycosis treatment.</p>