Bychinin MV, Klypa TV, Mandel IA, et al. - This study was undertaken to investigate the serum 25-hydroxyvitamin D [25(OH)D] concentration in patients admitted to the intensive care unit (ICU) as a predictor of coronavirus disease 2019 (COVID-19) mortality. Researchers performed a single-center retrospective observational study including a total of 40 adult patients (50% men) with confirmed COVID-19 who were admitted to the ICU. The Mann–Whitney test, Fisher's exact test, Kaplan–Meier analysis, and receiver operator characteristic analysis were used to evaluate serum 25(OH)D concentration as a predictor of COVID-19 mortality. As per the results, the ICU patients had a low serum 25(OH)D concentration. In patients with COVID-19, serum 25(OH)D concentrations ≤ 9.9 ng/mL on admission can be used to predict in-hospital mortality.