Sako K, et al. - Via retrospectively evaluation of 21,939 patients, researcher assessed whether recurrence of acute kidney injury (AKI) increases the risk of mortality, and evaluated the prognosis of recurrent AKI cases by setting 21 days as the cut-off period. A total of 510 developed the first AKI, among whom 151 developed recurrent AKI within 2 years. The rate of all-cause mortality in the early-recurrence patients was higher compared with non-recurrence or late-recurrence patients. Relatively poor prognosis was noted in patients who experienced recurrent AKI before 21 days from the first AKI. Thus, in order to detect a recurrence event for a better prognosis after AKI, careful follow-up for at least 21 days after AKI is warranted.