In this report, a case of adult onset fatal cerebral oedema as a rare complication of diabetic ketoacidosis (DKA) is described and confirmed at post-mortem pathological examination. The pathogenesis of cerebral oedema due to DKA is still unknown. Potential mechanisms include the administration of sodium bicarbonate leading to intracellular acidosis, excessive fluid infusion causing swelling of brain tissue, or reduction of plasma osmolarity by a rapid fall in glucose levels causing osmotic swelling.