Asthma exacerbations are a common and important cause of attendance at emergency departments (ED) and subsequent hospital admissions. Despite previous reviews reporting that in acute settings the risk of hospital admission is reduced with the use of high doses of inhaled corticosteroids (ICS), this evidence has not changed clinical practice. To estimate the efficacy of ICS in the treatment of acute asthma in ED. Randomized controlled trials were identified using PubMed, The Cochrane Library, and EMBASE. The primary outcome was hospital admission rates. The primary comparison was between administration of ICS in addition to systemic corticosteroids (SCS) and to SCS alone. Secondary comparisons were ICS alone compared with SCS alone and ICS compared with placebo. There were 25 studies involving 2733 participants. For the primary comparison, ICS in addition to SCS reduced the risk of hospital admission compared with SCS; fixed-effects odds ratio (95% confidence interval) 0.73 (0.57-0.94). Lung function was poorly reported. There was moderate evidence of an improvement in clinical scores and vital signs with ICS in addition to SCS. Relatively few studies reported adverse events. There is moderate evidence that high doses of ICS, in addition to SCS, reduce the risk of hospital admission in ED treatment of moderate-to-severe asthma exacerbations. Further research is required to determine their optimal role in both ED and outpatient settings.