Background/Aims: Patients with ulcerative colitis (UC) are at an increased risk of certain infections and malignancies compared with the general population. Incidence rates (IRs) of hospitalized infections, herpes zoster (HZ), and malignancies in patients with UC, stratified by treatment, in Japan were estimated. Methods: This retrospective study identified patients with UC treated with corticosteroids, immunosuppressants, or tumor necrosis factor inhibitors (TNFi) from 2 administrative databases (Japan Medical Data Center [JMDC] and Medical Data Vision [MDV]). IRs (unique patients with events per 100 patient‐years) were estimated for hospitalized infections, HZ, and malignancies, between June 2010 and May 2018. Results: Among 6,033 MDV patients with UC receiving corticosteroids, immunosuppressants, or TNFi, IRs (95% confidence intervals) were: hospitalized infections, 1.73 (1.52–1.93); HZ, 1.00 (0.85–1.16), and malignancies, 1.48 (1.29–1.66). Among 958 JMDC patients with UC receiving corticosteroids, immunosuppressants, or TNFi, IRs (95% confidence intervals) were: HZ, 1.82 (1.27–2.37) and malignancies, 1.35 (0.87–1.82). In both cohorts, IRs of malignancies were generally similar among patients receiving immunosuppressants, TNFi, or combination therapy (immunosuppressants and TNFi); this was also true for IRs of hospitalized infections and HZ in the MDV cohort. IRs of hospitalized infections, HZ, and malignancies were higher in patients receiving calcineurin inhibitors compared with immunosuppressants or TNFi, in both cohorts. Conclusions IRs of hospitalized infections, HZ, and malignancies among patients with UC were generally similar regardless of UC treatment, except for calcineurin inhibitors.