The purpose of this study is to evaluate the effectiveness and safety of ozanimod vs azathioprine for the treatment of ulcerative colitis (UC) in real-world clinical practice in Japan

Inclusion Criteria:

• Participants with Ulcerative Colitis (UC) provided written consent to participate in the study
• Participants who are aged ≥ 18 years at the earlier date of either initiation of treatment with ozanimod or azathioprine or obtaining consent
• Starting dose of oral steroid ≥ 30 mg/day (prednisolone equivalent)
• Administration of ozanimod or azathioprine started after oral steroid administration, and ozanimod or azathioprine administered concomitantly with steroids (excluding patients who started oral steroids and ozanimod or azathioprine on the same day)
• In the ozanimod group, patients with notable clinical symptoms due to the primary disease (rectal bleeding subscore ≥ 1 point or total PRO2 score ≥ 2 points) remained at the start of ozanimod administration
• In the azathioprine group, patients who started azathioprine treatment after February 2019

Exclusion Criteria:

• Participants with symptoms of UC with no change or increase in Patient-Reported Outcome 2 (PRO2) from the time of initiating oral steroid administration after 2 weeks of administration of ≥ 30 mg/day (prednisolone equivalent) of oral steroids
• Participants with complications requiring continued steroid use (excluding topically acting steroids for inhalation or topical application)
• Participants who participated in other clinical studies involving interventions during the observation period
• Participants judged to be inappropriate for enrollment in this study by the investigator at each participating study site

The study population will consist of adults diagnosed with ulcerative colitis (UC) who initiated ozanimod or azathioprine treatment after starting oral steroids and concomitant-use oral steroids in Japan