This is a multi-centre, randomised, double-blind, active treatment, parallel group induction study in subjects with moderately-to-severely active Crohn's disease. Subjects will receive one of two doses (500 milligrams once daily, 500 milligrams twice daily) of GSK1605786A for 12 weeks. The primary objective of the study is to induce clinical response (Crohn's Disease Activity Index [CDAI] decrease from baseline of at least 100 points) and/or remission (CDAI score less than 150) with GSK1605786A at Week 12 in subjects with active Crohn's disease to qualify subjects for enrolment into a 52 week maintenance study (CCX114157). Secondary objectives will include assessment of the safety and evaluation of the efficacy in induction of clinical response or remission. Safety will be assessed by recording of adverse events and assessment of changes in clinical laboratory parameters, vital signs and electrocardiogram. Population pharmacokinetics will evaluate the two doses of GSK1605786A. Health outcomes assessments will include changes in Inflammatory Bowel Disease Questionnaire, SF-36, EQ-5D, and Work Productivity and Activity Impairment-Crohn's Disease.