BACKGROUND: Upadacitinib (UPA) is a novel selective JAK inhibitor approved for adults with ulcerative colitis (UC) and with positive phase 3 data for Crohn's disease (CD). Pediatric off-label use is common due to delays in pediatric approvals; real-world data on UPA are needed to understand the safety and effectiveness in pediatric IBD. METHODS: This is a single-center retrospective case series study of adolescents (12-17 years) with inflammatory bowel disease IBD on UPA. The primary outcome was postinduction steroid-free clinical remission (SF-CR) defined as Pediatric UC Activity Index (PUCAI) or Pediatric CD Activity Index (PCDAI) </=10. Secondary outcomes include postinduction clinical response (decrease >/=12.5 in PUCAI/PCDAI), postinduction C-reactive protein (CRP) normalization, 6-month SF-CR, and intestinal ultrasound response and remission. Adverse events were recorded through last follow-up. RESULTS: Twenty patients (9 CD, 10 UC, 1 IBD-U; 55% female; median age 15 years, 90% >/=2 biologics) were treated with UPA for >/=12 weeks (median 51 [43-63] weeks). Upadacitinib was used as monotherapy in 55% and as combination with ustekinumab and vedolizumab in 35% and 10%, respectively. Week 12 SF-CR was achieved in 75% (15/20) and 80% (16/20) with CRP normalization. About 3/4 (14/19) achieved SF-CR at 6 months. Adverse event occurred in 2 patients (10%): Cytomegalovirus colitis requiring hospitalization and hyperlipidemia requiring no treatment. In the 75% with ultrasound monitoring, response and remission were achieved in 77% and 60%, respectively. CONCLUSION: While awaiting pediatric registration trials, our data suggest that UPA is effective in inducing and maintaining SF-CR in adolescents with highly-refractory IBD with an acceptable safety profile.