BACKGROUND This study aimed to clarify the accuracy of an in-hospital mortality prediction score for patients with hypothermia. The score consists of five variables (age ≥70 years, mean arterial pressure <90 mm Hg, pH < 7.35, creatinine >1.5 mg/dL, and confusion). In contrast to the previously reported population in southern Israel, a desert climate, we apply the score system to a Japanese humid subtropical climate. METHODS The study included patients with a principal diagnosis of hypothermia who were admitted to our community hospital between January 2008 and January 2019. Using the medical records from initial visits, we retrospectively calculated in-hospital mortality prediction scores along with sensitivity and specificity. RESULTS We recruited 69 patients, 67 of which had analyzable data. Among them, the in-hospital mortality rate was 25.4%. Hypothermia was defined as mild (32-35°C) in 34 cases (50.7%), moderate (28-32°C) in 23 cases (34.3%), and severe (<28°C) in 10 cases (14.9%). The C-statistics of the in-hospital mortality prediction score was 0.703 (95% confidence interval, 0.55-0.84) for thirty-day survival prediction. After adjustment of the cutoff point of each item with ROC analysis and selection of the variants, the C-statistics of the in-hospital mortality prediction score rose to 0.81 (95% confidence interval, 0.69-0.92). CONCLUSIONS The in-hospital mortality prediction scores showed slightly less predictive value than those in the previous report. With some modification, however, the score system could still be applied efficiently in the humid Japanese subtropical climate. An appropriate management strategy could be established based on the predicted mortality risk.