The objective of our study was to compare the safety and efficacy of discharging asthmatic children from hospital on three versus four hourly nebulized salbutamol. The setting was a tertiary referral paediatric hospital in Sydney, NSW, Australia. The design was a randomized controlled parallel group study. All children admitted to hospital with acute asthma and who were over 18 months of age were eligible to enter the study. Patients were excluded if they had non-English speaking parents, no telephone, or chronic cardiac or neurological disease. Children were treated according to standard asthma management but were randomly allocated to be discharged on three or four hourly nebulized salbutamol. Patients were surveyed using a telephone questionnaire 1 to 2 weeks after discharge. The primary outcome measure was re-presentation to the Emergency Department (ED) within 7 days. Other outcomes included readmission to hospital, re-presentation to the local doctor, parental satisfaction and length of hospital stay. A total of 63 children were enrolled in the study (32 in the three hourly group and 31 in the four hourly group). There were no re-presentations to the ED or hospital readmissions within 1 to 2 weeks in either group. However, re-presentations to the local doctor were common, 71.8% in the three hourly and 74.1% in the four hourly groups, respectively. These were predominantly for routine review. The mean (+/- SD) hospital length of stay was not significantly different between the three and four hourly groups, 48.94 (+/- 20.61) and 54.88 (+/- 32.59) hours, respectively (P = 0.672). Parents felt the timing of discharge was 'too early' in five (15.6%) of three hourly and five (16.1%) of four hourly patients. Three (9.7%) of the four hourly but none of the three hourly patients felt they were sent home 'later than necessary'. Five (15.1%) of the three hourly and three (9.7%) of the four hourly group parents did not feel comfortable looking after their child at home immediately after discharge. None of these differences were statistically significant. Discharge of asthmatic children from hospital on three hourly nebulized salbutamol is as safe and effective as on four hourly. Parents are generally very satisfied with timing of discharge, irrespective of frequency of nebulization. Earlier discharge benefits both the child and their family, and improves hospital bed utilization.