It is well recognized that medications have an important role to play in preventing relapse in bipolar disorder. The impact these treatments have on rates of admission to hospital in particular has been less well studied. We combined data on hospitalization from 11 randomized controlled trials in a network meta-analysis. We found that the published evidence demonstrates significant reductions in admission rates compared to placebo from lithium (risk ratio (RR) 0.44, 95% confidence interval (CI) 0.32-0.59), valproate (RR 0.50, 95% CI 0.28-0.90), a combination of lithium and valproate (RR 0.50, 95% CI 0.28-0.90), carbamazepine (RR 0.46, 95% CI 0.29-0.73) and olanzapine (RR 0.27, 95% CI 0.16-0.43). The evidence base contributing to these estimates remains fairly small, leading to broad confidence intervals for estimates of effect. More precise estimates could be obtained if unpublished outcomes data from other trials in this area became available. Several pharmacological treatments appear to be effective at reducing the need for hospital admission in people with bipolar disorder.