The objective of this study was to compare the efficacy of a single dose of oral dexamethasone of varying sizes in 120 children hospitalized with croup in two sequential double blind, randomized, controlled clinical trials (Trials A and B). The study was conducted in the Emergency Department Observation Ward of a tertiary pediatric hospital. One hundred and twenty children (age range 6 to 160 months) hospitalized with croup participated. Baseline characteristics for the two groups in each trial were similar. In Trial A 60 children received either 0.6 or 0.3 mg/kg dexamethasone syrup; in Trial B 60 children received either 0.3 or 0.15 mg/ kg dexamethasone syrup. Duration of hospitalization, reduction in croup scores, and adrenaline usage were evaluated. Median duration of hospitalization was similar for children in Trial A (7 and 8 hr), and in Trial B (9 and 9 hr). Croup scores following treatment did not differ and were significantly lower than initial scores for all groups and in each trial. Other outcome measures were similar for the two groups in each trial, including need for nebulized adrenaline, numbers of patients admitted to intensive care, rate of return to medical care with reoccurrence of croup, and readmission to hospital with croup following discharge from hospital. We conclude that oral dexamethasone in a dose of 0.15 mg/kg is as effective as 0.3 or 0.6 mg/kg in relieving symptoms and results in a similar duration of hospitalization in children with croup.