Objective: Neutralising pro-inflammatory interleukin-6 (IL-6) may effectively treat Crohn's disease (CD). Effects of PF-04236921, an anti-IL-6 antibody, in adults with CD are reported., Design: Parallel-group, dose-ranging, double-blind trial with 4-week screening and 12-week treatment periods. After induction, patients entered 28-week follow-up or 48-week open-label extension (OLE) with 28-week follow-up. Adults with confirmed CD and inadequate response to anti-tumour necrosis factor (TNF) therapy were included. Induction study : 249 patients randomised 1:1:1:1 to placebo, PF-04236921 10, 50 or 200 mg by subcutaneous injection on days 1 and 28. OLE study : PF-04236921 50 mg every 8 weeks up to six doses followed by 28-week follow-up., Results: 247 patients were randomised and received treatment in the induction study. The 200 mg dose was discontinued due to safety findings in another study (NCT01405196) and was not included in the primary efficacy analysis. Crohn's Disease Activity Index (CDAI)-70 response rates with PF-04236921 50 mg were significantly greater than placebo at weeks 8 (49.3% vs 30.6%, P<0.05) and 12 (47.4% vs 28.6%, P<0.05) and met the primary end point. Week 12 CDAI remission rates with PF-04236921 50 mg and placebo were 27.4% and 10.9%, respectively (16.5% difference; P<0.05). 191 subjects received treatment in the OLE. Common treatment-emergent and serious adverse events in both studies included worsening CD, abdominal pain and nasopharyngitis., Conclusions: PF-04236921 50 mg induced clinical response and remission in refractory patients with moderate-to-severe CD following failure of anti-TNF therapy. GI abscess and perforation were observed, a specific focus of attention during future clinical development., Trial Registration Number: NCT01287897 and NCT01345318., Competing Interests: Competing interests: SD is a speaker, consultant and advisory board member for Abbott Laboratories, AbbVie, Actelion, Alphawasserman, AstraZeneca, Cellerix, Cosmo Pharmaceuticals, Ferring, Genentech, Grunenthal, Hospira, Johnson and Johnson, Merck & Co, Millennium Takeda, Mundipharma, Novo Nordisk, Nycomed, Pharmacosmos, Pfizer, Schering-Plough, UCB Pharma and Vifor. SV received research support from AbbVie, MSD and Takeda and received consultancy and/or speaker honoraria from AbbVie, Celgene, Centocor, Ferring, Galapagos, Genentech/Roche, Hospira, MSD, Mundipharma, Pfizer, Shire and Takeda. PH is a consultant and/or advisory board participant for, and/or has received speaker honoraria, research support and/or educational grants from, Cubist, Evoke, Ferring, Forest, Furiex, Gilead, GlaxoSmithKline, Intercept, Ironwood, Menarini, Nature Coast Clinical Research, Pfizer, Rhythm, Salix, Synergy, Takeda, Theravance and Vivus. RP is a consultant for and/or received lecture fees from Abbott, AbbVie, Allergan, Amgen, AstraZeneca, Axcan Pharma, Biogen Idec, Bristol-Myers Squibb, Centocor, ChemoCentryx, Eisai Medical Research, ELAN, Ferring, Genentech, GlaxoSmithKline, Janssen, Millennium, MSD, Ocera Therapeutics, Otsuka America Pharmaceuticals, Pfizer, Shire Pharmaceuticals, Prometheus, Robarts Clinical Trials, Schering-Plough, Synta Pharmaceuticals, Takeda, Teva, UCB Pharma and Warner Chilcott. GR is a consultant for Abbott, AbbVie, Augurix, Boehringer, Calypso, FALK, Ferring, Fisher, Genentech, Essex/MSD, Novartis, Pfizer, Phadia, Roche, Takeda, Tillots, UCB, Vifor, Vital Solutions and Zeller; received speaker honoraria from AstraZeneca, Abbott, AbbVie, FALK, MSD, Phadia, Tillots, UCB and Vifor; and received educational grants and research grants from Abbot, AbbVie, Ardeypharm, Augurix, Calypso, Essex/MSD, FALK, Flamentera, Novartis, Roche, Takeda, Tillots, UCB and Zeller. AK received educational grants from AbbVie, MSD and Takeda. PD participated in advisory boards for, and received fees and grants from, AbbVie, Biofortis, BioMérieux Danone, Ferring, Genfit, Intralytix, Kitozyme, Lesaffre, MSD, Norgine, OmegaPharma International, Pileje, PPM, Roquette, Takeda and TxCell. RWL participated in advisory boards for AbbVie, Aspen, Ferring, Janssen, Hospira and Takeda and received research support from Janssen, NHMRC Career Development Fellowship and Shire. SS received consultancy fees from AbbVie, Bristol-Myers Squibb, Boehringer, Ferring, Genentech/Roche, Pfizer, MSD/Janssen, Takeda and UCB and lecture fees from AbbVie, MSD/Janssen, Takeda and UCB. AB, MKM, CL, NR and JB are all employees of Pfizer Inc and hold stock or options in Pfizer Inc. GMC and FC are former employees of Pfizer Inc and FC is a current employee of Shire Pharmaceuticals. GF has no conflicts of interest to report. GMC has been a consultant for Adare, Albireo, AstraZeneca, CinRx, Cutis, OrphoMed, Second Genome, Strongbridge and Zealand., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2019. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)