OBJECTIVE To characterize the effect of upadacitinib 15 mg once daily (UPA15) on enthesitis in patients with psoriatic arthritis from the SELECT-PsA Phase 3 trials. METHODS Patients with an inadequate response/intolerance to ≥ 1 non-biologic DMARD (SELECT-PsA 1) or ≥ 1 biologic DMARD (SELECT-PsA 2) received UPA15, adalimumab 40 mg every other week or placebo (weeks 0-24) switched to UPA15 (week 24 onward). The Leeds Enthesitis Index (LEI) and Spondyloarthritis Research Consortium of Canada (SPARCC) index were used to assess improvement in enthesitis, enthesitis resolution, maintenance of enthesitis resolution, and protection from enthesitis development through week 56. RESULTS Data from 639 patients receiving UPA15 and 635 patients receiving placebo (including 317 patients who switched from placebo to UPA15) were analysed. UPA15 led to higher rates of enthesitis resolution vs placebo at week 24 (LEI: 59.8% vs 38.0%; SPARCC index: 50.6% vs 31.5%, respectively) and greater improvements in the LEI (-1.7 vs -1.0) and SPARCC index (-3.4 vs -1.9); improvements were maintained through week 56. Improvements were observed after 12 weeks of UPA15 treatment. Over 90% of patients without enthesitis (LEI = 0) at baseline receiving UPA15 were enthesitis-free at week 56, and UPA15 prevented recurrence of enthesitis at week 56 in > 80% of patients with enthesitis at baseline who achieved resolution (LEI = 0) at week 24. CONCLUSIONS UPA15 is associated with a comprehensive improvement in enthesitis, with improvements observed after 12 weeks of treatment. Additionally, treatment with UPA15 was associated with maintaining an enthesitis-free state after resolution and protection against new-onset enthesitis. BACKGROUND NCT03104400 (SELECT-PsA 1) and NCT03104374 (SELECT-PsA 2).