Evaluate the cost and clinical impacts of rapid whole-exome sequencing (rWES) for managing pediatric patients with unknown etiologies of critical illnesses through an expert elicitation experiment. Physicians in the intervention group (n = 10) could order rWES to complete three real-world case studies, while physicians in the control group (n = 8) could not. Costs and health outcomes between and within groups were compared. The cost incurred in the intervention group was consistently higher than the control by 60,000-70,000 THB. Fewer other investigation costs were incurred when rWES could provide a diagnosis. Less cost was incurred when an rWES that could lead to a change in management was ordered earlier. Diagnostic accuracy and the quality of non-pharmaceutical interventions were superior when rWES was available. In acute pediatric settings, rWES offered clinical benefits at the average cost of 60,000-70,000 THB. Whether this test is cost-effective warrants further investigations. Several challenges, including cost and ethical concerns for assessing high-cost technology for rare diseases in resource-limited settings, were potentially overcome by our study design using expert elicitation methods.