Incidence of cases per month.

Testicular torsion is a severe urological emergency caused by the twisting of the spermatic cord. The nationwide incidence of testicular torsion in Japan has not been previously reported. Accordingly, we aimed to estimate the nationwide incidence of testicular torsion using the National Database of Health Insurance Claims and Specific Health Checkups of Japan (NDB) and examine the orchiectomy rate. This cross-sectional study was based on data from the NDB. We extracted data of patients aged < 21 years with documented testicular torsion and relevant treatment from January 2018 to December 2020. Testicular torsion was identified based on the Japanese standardized disease codes. The national incidence rate between 2018 and 2020 was calculated and assessed according to age and region of origin. Orchiectomy rates were evaluated according to age. The nationwide incidence rates of testicular torsion were 14.46, 15.09, and 15.88 per 100,000 males aged < 21 years in 2018, 2019, and 2020, respectively. The orchiectomy rate was 7.1%. Testicular torsion was most frequently observed during winter. A similar trend was observed nationwide. To the best of our knowledge, this study is the first to report the nationwide incidence of testicular torsion in Japan.