Abstract Background and Aims This GEMINI 1 post hoc analysis evaluated vedolizumab efficacy for inducing deep remission in patients with ulcerative colitis and correlation between vedolizumab trough concentrations and deep remission rates. Methods Week 6 vedolizumab responders were re-randomized to placebo or vedolizumab every 8 or 4 weeks. Deep remission at Week 52 was measured using four different definitions from most to least stringent: 1 Mayo Clinic endoscopic score = 0, rectal bleeding score = 0 and decrease or no change from baseline in stool frequency score; 2 endoscopic score ≤1, rectal bleeding score = 0 and stool frequency score = 0; 3 endoscopic score ≤1, rectal bleeding score = 0, decrease or no change from baseline stool frequency score, and total score endoscopic score + rectal bleeding score + stool frequency score ≤1; and 4 endoscopic score ≤1, rectal bleeding score = 0 and stool frequency score ≤1. Steady-state trough vedolizumab serum concentrations were evaluated. Results At Week 6, 373 vedolizumab responders were re-randomized to maintenance placebo n = 126 or vedolizumab every 8 n = 122 or 4 n = 125 weeks. Significantly more vedolizumab patients achieved deep remission at Week 52 for the most (placebo 8.7%, every 8 weeks 27.0% p = 0.0001, every 4 weeks 28.0% p < 0.0001) and least (placebo 15.9%, every 8 weeks 43.4% p < 0.0001, every 4 weeks 43.2% p < 0.0001) stringent definitions. Patients with higher vedolizumab trough concentration quartiles had higher deep remission rates all definitions compared with those with the lowest quartile or who received placebo. Conclusion Vedolizumab was associated with significantly higher deep remission rates than placebo at Week 52, regardless of deep remission definition NCT00783718.