This is a multi-centre, double-blind, randomised, active treatment, parallel group study designed to induce clinical response and/or clinical remission with two oral doses of GSK1605786A (500 milligrams once daily, 500 milligrams twice daily) over a 12-week treatment period in subjects with moderately-to-severely active Crohn's disease. The primary objective of this study is to qualify subjects for enrolment into a follow up 52 week maintenance study CCX114157. Subjects who achieve induction of clinical response (CDAI decrease from baseline of at least 100 points) or remission (CDAI score less than 150) at Week 12 following treatment with GSK1605786A will be eligible for enrolment into the maintenance study CCX114157. Secondary objectives will include assessment of the safety and evaluation of the efficacy in induction of clinical response or remission.