Therapeutic hypothermia (TH) is considered as a treatment option in patients with stroke and brain injury for controlling intracranial pressure. A relatively longer duration of TH is required in such patients than in cardiac arrest patients. We aimed to investigate blood glucose parameters during TH that predict unfavorable neurological outcomes and mortality in patients admitted to the neurological or neurosurgical intensive care unit (ICU). This retrospective study evaluated electronic medical records of patients admitted to the ICU from January 1, 2012, to May 20, 2017. A total of 103 patients were included in the analyses. Multivariable analyses revealed that age and glycemic variability (GV) index were significantly associated with poor neurological outcomes (odds ratio [OR] 1.09, 95% confidence interval [CI] 1.03-1.15, p = 0.002, and OR 1.04, 95% CI 1.02-1.06, p < 0.001, respectively); furthermore, cumulative input-output balance, sequential organ failure assessment score, and glucose variability index were associated with 90-day mortality (hazard ratio [HR] 1.13, 95% CI 1.05-1.21, p < 0.001; HR 1.20, 95% CI 1.04-1.38, p = 0.010; and HR 1.01, 95% CI 1.01-1.02, p < 0.001, respectively). Receiver operating characteristic curve analyses of the GV index for prediction of 90-day mortality and poor neurological outcomes revealed that the areas under the curves were 0.747 (95% CI 0.65-0.85) and 0.826 (95% CI 0.75-0.91), respectively. In conclusion, variability in glucose levels may be valuable for predicting 90-day mortality and poor neurological outcomes in patients undergoing long-term TH.