Central pontine myelinolysis (CPM) is a rare demyelinating condition which has been reported to occur in a variety of clinical settings, but most commonly in association with a rapid rise in plasma osmolality during correction of chronic hyponatremia. The clinical consequences can vary from a mild motor weakness that resolves completely over time to the devastating locked-in syndrome. In this presentation, we report a case of hyperosmolar hyperglycemic syndrome (HHS) with ponto-occipital disintegration. A 71-year-old female was transferred to our ER by an ambulance due to consciousness disorder and continuous fever for 10 days. We diagnosed septic shock caused by urinary tract infection (UTI), cerebral multiple infarctions, acute kidney injury (AKI) and HHS without treatment for diabetes. Then, we started therapeutic interventions for them based on the guideline with severe control for blood sugar (BS; primary 1635 mg/dl) under insulin therapy and hypernatremia (primary 153 mEq/l) under crystal infusion control in advanced care unit, apparently on routine lab data. However, the initial serum sodium value of 153 mEq/l was slowly compensated to 148 mEq/l in 60 hours under guideline on routine lab data, the initial compensated sodium value with osmolality was changed from 178 mEq/l to 150 mEq/l in the period. She recovered from her primary diagnosis and unconsciousness. After stabilized sepsis and HHS, we detected CPM on brain MRI due to following up multiple cerebral infarctions with left leg paralysis and verbal disorder. She gradually recovered over several months with intensive rehabilitation and eventually regained near normal functional capacity with stabilized BS. When we consider HHS with hypernatremia, it may be necessary to pay attention to not only to BS control and sodium control according to the guideline but also to osmolality changes to prevent CPM.