Four insulin-treated diabetic patients presented over a 2-year period in hypoglycaemic coma and died secondary to this. At autopsy, there were widespread neuropathological changes, in all four cases consistent with hypoglycaemic damage. Abnormalities were also found in areas regarded as generally being spared in hypoglycaemic brain injury, particularly the brain stem, thalamus, globus pallidus, and cerebellum, and these lesions may relate to seizure activity and cardio-respiratory depression secondary to the hypoglycaemia. Although more than one aetiological factor may be contributing, it is concluded that the neuropathological changes in diabetic patients dying in hypoglycaemic coma are extremely diverse.