BACKGROUND: The spread of coronavirus disease 2019 (COVID-19) had a major impact on the health of people worldwide. The clinical background and clinical course of inflammatory bowel disease (IBD) among Japanese patients with COVID-19 remains unclear. METHODS: This study is an observational cohort of Japanese IBD patients diagnosed with COVID-19. Data on age, sex, IBD (classification, treatment, and activity), COVID-19 symptoms and severity, and treatment of COVID-19 were analyzed. RESULTS: From 72 participating facilities in Japan, 187 patients were registered from June 2020 to October 2021. The estimated incidence of COVID19 in Japanese IBD patients was 0.61%. The majority of IBD patients with COVID-19 (73%) were in clinical remission. According to the WHO classification regarding COVID-19 severity, 93% (172/184) of IBD patients had non-severe episodes, while 7% (12/184) were severe cases including serious conditions. 90.9% (165/187) of IBD patients with COVID-19 had no change in IBD disease activity. A logistic regression analysis stepwise method revealed that older age, higher body mass index (BMI), and steroid use were independent risk factors for COVID-19 severity. Six of nine patients who had COVID-19 after vaccination were receiving anti-tumor necrosis factor (TNF)-α antibodies. CONCLUSION: Age, BMI and steroid use were associated with COVID-19 severity in Japanese IBD patients.