Ustekinumab is a monoclonal antibody that binds with high affinity to the p40 subunit of human interleukin 12 (IL12 and IL23) that has been approved for treatment of patients with moderate to severe Crohn’s disease (CD). However, there are few data on its pharmacokinetic properties or the relationship between drug exposure levels and patient response. We collected data from 2 phase 3 induction studies and 1 maintenance study to determine ustekinumab’s pharmacokinetic features, relationship between exposure and response, and optimal serum concentrations for efficacy.