The use of glucocorticosteroids to treat both Crohn's disease (CD) and ulcerative colitis (UC) is widespread, but no systematic review and meta-analysis has examined the issue of efficacy of these agents in its entirety. MEDLINE, EMBASE, and the Cochrane central register of controlled trials were searched (through December 2010). Randomized controlled trials (RCTs) recruiting adults with active or quiescent CD comparing standard glucocorticosteroids or budesonide with placebo or each other, or comparing standard glucocorticosteroids with placebo in active UC, were eligible. Dichotomous data were extracted to obtain relative risk (RR) of failure to achieve remission in active disease, and RR of relapse of activity in quiescent disease, with a 95% confidence interval (CI). Adverse events data were extracted where reported. The search identified 3,061 citations, and 20 trials were eligible. Only one trial was at low risk of bias. Standard glucocorticosteroids were superior to placebo for UC remission (RR of no remission=0.65; 95% CI 0.45-0.93). Both trials of standard glucocorticosteroids in CD remission reported a statistically significant effect, but because of heterogeneity between studies, the overall effect was not significant (RR=0.46; 95% CI 0.17-1.28). Budesonide was superior to placebo for CD remission (RR=0.73; 95% CI 0.63-0.84), but not in preventing CD relapse (RR=0.93; 95% CI 0.83-1.04). Standard glucocorticosteroids were superior to budesonide for CD remission (RR=0.82; 95% CI 0.68-0.98), but glucocorticosteroid-related adverse events were commoner (RR=1.64; 95% CI 1.34-2.00). Standard glucocorticosteroids are probably effective in inducing remission in UC, and may be of benefit in CD. Budesonide induces remission in active CD, but is less effective than standard glucocorticosteroids, and is of no benefit in preventing CD relapse.