Abstract Background Clinical trials may not readily reflect clinical practice. We aimed to assess the clinical effectiveness of vedolizumab in a real-world cohort of patients with ulcerative colitis (UC). Methods This is a prospective, observational, multi-centre cohort study. Eligible patients had active UC confirmed by a Mayo endoscopic subscore ≥2 at initiation of vedolizumab and had started treatment from 1/6/2015. Exclusion criteria included concurrent participation in a clinical trial in which UC treatment is dictated and contraindications to vedolizumab. All patients provided a written consent. Data on clinical characteristics, treatment patterns, disease activity and the short health scale were recorded at baseline and prospectively, using an electronic Case Record Form, integrated with the Swedish National Quality Registry for IBD (SWIBREG). The primary outcomes were A) clinical response, defined as a decrease in partial Mayo score of ≥2 and a reduction of ≥25 % from baseline, with a decrease ≥1 on the rectal bleeding score or an absolute rectal bleeding score of 0 or 1, at week 12 and B) clinical remission, defined as a partial Mayo score <2, at week 52. Continuous data are presented as median (interquartile range). Differences between baseline and follow-up visits were assessed by the Wilcoxon-signed rank test. Results In total, 117 eligible UC patients were included during the study period 1/6/2015 to 2/6/2018. Clinical and demographical characteristics of patients are shown in Table 1; 101/117 (86%) patients had failed prior anti-TNF therapy. The drug persistence rate was 106/117 (91%) at 12 weeks and 79/117 (68%) at 52 weeks. The clinical response rate at 12 weeks was 59/117 (50%) and the clinical remission rate at 52 weeks was 57/117 (49%). Altogether, 35/117 (30%) had an endoscopic Mayo score ≤1 at 12 weeks and 41/117 (35%) at 52 weeks. However, data on endoscopy were not available for 42 vedolizumab treated patients at 12 weeks and 30 at 52 weeks. Among patients who continued vedolizumab, the median partial Mayo score decreased from 4 (3–5) at baseline to 1 (0–2) at 52 weeks (p < 0.0001). Correspondingly, the median faecal calprotectin decreased from 646 (333–1130) µg/g to 162 (42–382) µg/g (p = 0.0002) and the median C-reactive protein from 5.0 (2.1–8.0) mg/L to 3.5 (1.6–5.0) mg/L (p = 0.008). Consistently, quality of life improved in vedolizumab treated patients, with a significant reduction of the overall short health scale score at 52 weeks (p < 0.0001). Conclusion Vedolizumab treated patients with UC represented a treatment-refractory group. Long-term (52 weeks) effectiveness of vedolizumab can be achieved, in terms of clinical- and inflammatory activity as well as in quality of life. The study was financially supported by Takeda.