Since the initial publication of this systematic review in 1997, several randomized trials examining the benefit of glucocorticoids have been published. The objective of this review is to provide evidence to guide clinicians in their treatment of patients with croup by determining the effectiveness of glucocorticoids and to identify areas requiring future research.To determine the effect of glucocorticoids for children with croup.We searched CENTRAL (2010, Issue 3), which contains the Cochrane Acute Respiratory Infections Group's Specialised Register, MEDLINE (1966 to July week 2, 2010) and EMBASE.com (1974 to July 2010). We also contacted authors of identified croup trials published in the last 10 years to inquire about additional published or unpublished trials.Randomised controlled trials (RCTs) that examine children with croup and objectively measure the effectiveness of glucocorticoids.Two review authors identified studies for potential relevance based on the review of the title and abstract (when available). Two review authors independently reviewed studies for relevance using a priori inclusion criteria and assessed trial quality. Differences were resolved by consensus. One review author extracted data using a structured form and another review author checked the results for accuracy. We performed standard statistical analyses.Thirty-eight studies were included (n = 4299). Glucocorticoids were associated with an improved Westley score (maximum 17 points) at six hours with a mean difference of -1.2 (95% confidence interval (CI) -1.6 to -0.8) and at 12 hours -1.9 (95% CI -2.4 to -1.3); at 24 hours this improvement was no longer significant (-1.3, 95% CI -2.7 to 0.2). Fewer return visits and/or (re)admissions occurred in participants treated with glucocorticoids (risk ratio (RR) 0.5; 95% CI 0.3 to 0.7). Length of time spent in accident and emergency or hospital (mean difference 12 hours, five to 19 hours) was significantly decreased for participants treated with glucocorticoids. Use of epinephrine decreased for children treated with a glucocorticoid (risk difference 10%; 95% CI 1 to 20).Dexamethasone and budesonide are effective in relieving the symptoms of croup as early as six hours after treatment. Fewer return visits and/or (re)admissions are required and the length of time spent in hospital is decreased. Research is required to examine the most beneficial method for disseminating croup practice guidelines and to increase the uptake of evidence.