Objective: Bronchiolitis is the most common lower respiratory tract infection in infants and the leading cause of hospitalisation. We aimed to assess whether intravenous hydration (IVH) was more cost-effective than nasogastric hydration (NGH) as a planned secondary economic analysis of a randomised trial involving 759 infants (aged 2–12 months) admitted to hospital with a clinical diagnosis of bronchiolitis and requiring non-oral hydration. No Australian cost data exist to aid clinicians in decision-making around interventions in bronchiolitis. Methods: Cost data collections included hospital and intervention-specific costs. The economic analysis was reduced to a cost-minimisation study, focusing on intervention-specific costs of IVH versus NGH, as length of stay was equal between groups. All analyses are reported as intention to treat. Results: Intervention costs were greater for IVH than NGH ($113 vs $74; cost difference of $39 per child). The intervention-specific cost advantage to NGH was robust to inter-site variation in unit prices and treatment activity. Conclusion: Intervention-specific costs account for <10% of total costs of bronchiolitis admissions, with NGH having a small cost saving across all sites.