Ustekinumab, a monoclonal antibody of interleukin-12 and interleukin-23, was approved for the treatment of moderate to severe Crohn’s disease (CD) in 2016. Ustekinumab is approved in CD for a weight-based IV induction dose followed by every 8 weeks of subcutaneous dosing. Response rates by 6 weeks range from 34% (anti-TNF failures) to 56% in bio-naïve patients. The remainder includes patients who partially-respond (PR) or do not respond (NR). Response by week 16 is 55% (anti-TNF failures) and 73% in bio-naïve patients suggestive of a ‘delayed response’ in some.