Patients with diabetes mellitus exhibit particular susceptibility to three severe infections of the head and neck: rhinocerebral mucormycosis, postoperative endophthalmitis, and malignant otitis externa. Rhinocerebral mucormycosis is an extensive life-threatening infection beginning in the nasal passages and sinuses and extending often into the orbit and the cerebrum. Endophthalmitis, which is infection of the vitreal contents, can occur secondary to bacteremia, trauma, or postoperatively. Invasive external otitis or malignant otitis externa is an invasive infection beginning in the adjacent soft tissue and into bone. It is usually secondary to Pseudomonas aeruginosa and occurs almost exclusively in diabetics. These will all be discussed in this article.