Background  The use of placebo in randomized clinical trials (PC-RCTs) is often required to evaluate drug efficacy in maintenance of Crohn’s disease (CD).

Aim  To determine pooled estimates of placebo rates of maintaining clinical remission and endoscopic recurrence following surgery for CD and identify factors that influenced placebo outcomes.

Methods  We performed a systematic review and meta-analysis of PC-RCTs evaluating post-operative maintenance therapies for CD identified from MEDLINE from 1966 to 2005.

Results  Twelve studies met our inclusion criteria. The pooled placebo rate of maintaining clinical remission was 56% (95% CI 47–64%; range 34–89%) during a median follow-up of 52 weeks (range 12–156 weeks), but significant heterogeneity existed among the studies (< 0.001). Prior steroid therapy was the only factor found to be associated with maintaining remission (= 0.04). The pooled placebo endoscopic recurrence rate was 58% (95% CI 51–65%; range 36–80%) during a median follow-up of 52 weeks (range 12–156 weeks), with significant heterogeneity noted (= 0.0003). Prior surgery, concomitant small bowel and colonic disease, fistulizing phenotype, or prior immunomodulator therapy influenced endoscopic recurrence (< 0.05).

Conclusion  Placebo rates in PC-RCTs evaluating post-operative clinical and endoscopic recurrence demonstrate significant variability, which is influenced by specific study characteristics.