Objectives: Despite little supporting data, thiopurine use is common in pediatric ulcerative colitis (UC). Our aim was to determine outcome following thiopurine use in a multicenter inception cohort of children diagnosed with UC. Methods: Data were obtained from a prospective observational study of newly diagnosed children 16 years of age. Data are recorded at diagnosis, 30 days, and quarterly. Patients are managed by physician dictates not protocol. Disease activity is classified by physician global assessment. The primary outcome was corticosteroid (CS)-free inactive UC at 1 year following thiopurine initiation without the need for rescue therapy (infliximab, calcineurin inhibitors, or colectomy). Results: Of 1,490 patients in our registry, 394 have UC (mean age at diagnosis 11.33.7 years); 197 (50%) received thiopurine (49% 3 months from diagnosis). Also, 84% were receiving CSs and 60% 5-aminosalicylates at thiopurine start. Of the 197 patients, there was insufficient follow-up (41), previous or concomitant use of infliximab (16), or calcineurin inhibitor (7), leaving 133 patients evaluable at 1 year. Of these, 65 (49%) had CS-free inactive UC without rescue therapy. CS-free inactive disease at 1 year after initiating thiopurine was not affected by starting thiopurine 3 months vs. 3 months from diagnosis, gender, age, or concomitant treatment with 5-aminosalicylates. Kaplan-Meier analysis showed that the likelihood of remaining free of rescue therapy in the thiopurine-treated patients was 73% at 1 year. Conclusions: Approximately 50% of children with UC starting thiopurine without previous or concomitant biologic or calcineurin inhibitor therapy have CS-free inactive disease 1 year later without the need for rescue therapy.