Central pontine myelinolysis (CPM) is well recognized to occur in a variety of clinical settings, but particularly following rapid correction of severe hyponatraemia. The development of CPM as a result of rapid shifts in plasma osmolality during the treatment of the hyperglycaemic hyperosmolar state (HHS) has hitherto been described in only one case. We report a second case in which this complication occurred in association with treatment of the HHS. The patient was a 49-year-old woman who presented to another hospital with drowsiness and a plasma glucose of 106 mmol/L. Her admission plasma sodium was 135 mmol/L. She received treatment with intravenous insulin and 0.9% normal saline, and there was a rapid drop in plasma glucose by 60 mmol/L within 6 h, which was associated with a rebound rise of plasma sodium to 159 mmol/L. Her plasma glucose and sodium were later stabilized. When the patient was transferred to our hospital a few days later, she was noted to have flaccid quadraparesis and pseudobulbar palsy. A magnetic resonance imaging scan revealed a pontine lesion consistent with CPM. She made a gradual recovery over several months with intensive rehabilitation and eventually returned to near normal functional capacity. This is the second case report in the literature of CPM complicating the management of HHS and highlights the importance of the judicious and measured correction of hyperglycaemia and the appropriate management of fluid replacement and electrolyte balance when treating this condition.