We present a fatal case of fulminant type 1 diabetes mellitus that was initially diagnosed as upper respiratory tract infection based on pharyngeal redness at a clinic. However, the patient then went into cardiopulmonary arrest, and was transferred to our hospital for treatment. Testing revealed very high levels of blood glucose (86.9 mmol/l), urinary glucose (2+) and ketones (4+). His glycosylated haemoglobin level was almost normal (6.2%; normal <6.2%). Autopsy revealed marked depletion and atrophy of the islets of Langerhans.