Tofacitinib is an oral, small-molecule Janus kinase inhibitor that is being investigated for IBD. We evaluated the efficacy and safety of tofacitinib for induction and maintenance treatment in patients with moderate-to-severe Crohn's disease (CD). We conducted two randomised, double-blind, placebo-controlled, multicentre phase IIb studies. Adult patients with moderate-to-severe CD were randomised to receive induction treatment with placebo, tofacitinib 5 or 10 mg twice daily for 8 weeks. Those achieving clinical response-100 or remission were re-randomised to maintenance treatment with placebo, tofacitinib 5 or 10 mg twice daily for 26 weeks. Primary endpoints were clinical remission at the end of the induction study, and clinical response-100 or remission at the end of the maintenance study. 180/280 patients randomised in the induction study were enrolled in the maintenance study. At week 8 of induction, the proportion of patients with clinical remission was 43.5% and 43.0% with 5 and 10 mg twice daily, respectively, compared with 36.7% in the placebo group (p=0.325 and 0.392 for 5 and 10 mg twice daily vs placebo). At week 26 of maintenance, the proportion of patients with clinical response-100 or remission was 55.8% with tofacitinib 10 mg twice daily compared with 39.5% with tofacitinib 5 mg twice daily and 38.1% with placebo (p=0.130 for 10 mg twice daily vs placebo). Compared with placebo, the change in C-reactive protein from baseline was statistically significant (p<0.0001) with 10 mg twice daily after both induction and maintenance treatments. Primary efficacy endpoints were not significantly different from placebo, although there was evidence of a minor treatment effect. No new safety signals were observed for tofacitinib. NCT01393626 and NCT01393899. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.