The main purpose of this study is to determine whether additional ustekinumab treatment is beneficial in patients with moderately to severely active Crohn's disease who initially had a clinical response to IV ustekinumab in one of the 2 initial induction studies (the CNTO1275CRD3001 \["UNITI-1"\] or CNTO1275CRD3002 \["UNITI-2"\] induction studies). The maintenance treatment will be injections in the skin (given subcutaneously, or "SC") of 90 mg ustekinumab either every 8 weeks or 12 weeks, and the effects (both the benefits and any side effects or adverse events) will be compared to SC placebo injections (otherwise identical except without ustekinumab). Patients who responded to IV ustekinumab in the UNITI-1 (NCT01369329) or UNITI-2 (NCT01369342) induction studies will be put into one of these 3 groups by chance (randomly, like rolling dice). The study will be double-blinded (so that neither patients nor study personnel know the identity of the assigned treatment). Patients who are randomized to either SC placebo or 90mg ustekinumab SC every 12 weeks who experience worsening in their Crohn's Disease symptoms (per the study loss of response criteria) will have their treatment adjusted so that they will instead start to receive 90mg ustekinumab SC every 8 weeks. All patients from the UNITI-1 or UNITI-2 studies (in addition to the patients described above who responded to IV ustekinumab) will be eligible to enter this study, provided the Week 8 visit in those trials was completed and study requirements are still met. Patients who are not in clinical response to IV placebo or ustekinumab in UNITI-1 or UNITI-2 will receive both IV and SC study agent at the first visit of this study (week 0). Patients previously receiving IV placebo will receive ustekinumab 130 mg IV at week 0 (and SC placebo), and patients previously receiving IV ustekinumab will receive 90 mg ustekinumab SC at week 0 (as well as IV placebo). If these patients are in clinical response 8 weeks later, they will receive 90 SC ustekinumab at that week8 visit, and will continue to receive Ustekinumab (every 8 weeks for participants not in response to IV Ustekinumab and every 12 weeks for participants not in response to IV Placebo) throughout the rest of the study (provided they otherwise remain eligible). Patients in clinical response to IV placebo induction dosing will continue to receive SC placebo. The main part of this study, also called the maintenance portion, will last 44 weeks. After week 44, all participants who are continuing to do well will be eligible to continue to receive study agent in the second part of the study, a long term extension where the study agent will continue to be administered up to week 252. Participants who discontinue study agent, either during the study, or after week 252, will be asked to return for a final safety follow-up visit 20 weeks after they last received study agent.

Patients in response to IV ustekinumab will be randomized to receive either placebo (Group 1), Ustekinumab 90 mg SC every 12 weeks (Group 2), or Ustekinumab 90mgSC every 8 weeks (Group 3). If patients in Groups 1 or 2 lose response, they will cross over to receive ustekinumab 90mg every 8 weeks. Other populations (nonresponders to prior IV ustekinumab or IV placebo) will receive ustekinumab at Week0 (either 90mg SC or 130mg IV, respectively) and continue SC ustekinumab if in response at Week 8, Placebo IV responders will continue to receive Placebo SC q4w.