Gau M, Konishi K, Takasawa K, et al. - This study was sought to verify the clinical details of salt wasting in newborn 21‐hydroxylase deficiency (21OHD) patients. Researchers retrospectively examined the conditions of classical 21OHD neonates before the initiation of therapy, based on the follow‐up survey of the screening in Tokyo from 1989 to 2017. This study examined a total of 100 classical 21OHD patients (55 male, 45 female). The findings demonstrated that the risk of developing severe salt‐wasting (SSW) increases during the second week of life without a threshold, and for preventing SSW, early intervention, ideally during the first week of life, is desirable. In the second week of life, increased body weight indicates the absence of SSW.