Ustekinumab is a monoclonal antibody against IL-12 and IL-23. Three phase III trials have now shown that ustekinumab is effective as an induction and maintenance therapy for Crohn's disease. In two 8 week induction trials, UNIT-1 (n = 741) and UNIT-2 (n = 628), patients with moderate to severe Crohn's disease received either placebo or a single intravenous dose of ustekinumab. In both trials, those receiving one of two doses of ustekinumab had a significantly (P ≤0.003) higher rate of response after 6 weeks than placebo. Patients who responded then participated in the IM-UNITI trial (n = 397), receiving maintenance subcutaneous injections of either ustekinumab or placebo. After 44 weeks, significantly more patients receiving ustekinumab were in remission than placebo (P = 0.005 and P = 0.04 for 8 week and 12 week regimens, respectively). Adverse events were similar among all treatment groups.