Objective The management of low-risk febrile neutropenia (FN) patients through ambulatory programs has demonstrated comparative safety and effectiveness to in-patient strategies. However, there is limited evidence of benefits of changing practice, particularly on a national scale. The aim of this study was to estimate costs and benefits of the program over a 10-year time horizon. Methods A comparative cost analysis from a health system perspective was performed, comparing costs and length of stay (LOS) of patients enrolled in an ambulatory program to a historical cohort who did not receive the program. Generalised linear models were used for analysis and bootstrapped to account for uncertainty. National data of identified FN admissions were used to inform future projections, with varying proportions of low-risk patients and eligibility for the ambulatory program. Results The overall LOS for patients in ambulatory cohort was 1.9 days shorter (95% confidence interval (CI) 1.0-2.8 days), a 50% reduction in in-patient bed-days. Although patients in the ambulatory cohort incurred additional costs due to care received outside hospital (mean (± s.d.) A$828.03 ± 124.30), the mean total cost incurred remained substantially lower than that of the historical cohort (A$2979 lower; 95% CI A$772-5391). On a national scale, this could translate into A$62.7 million in costs averted and 41347 bed-days saved over 10 years if the low-risk prediction rate and eligibility for ambulatory programs remained at currently observed rates. Conclusions The wider implementation of a safe and effective ambulatory program to manage low-risk FN patients can result in significant return-on-investment for the healthcare system by eliminating avoidable costs due to unnecessary lengthy hospital admissions. What is known about the topic? There is strong evidence demonstrating out-patient treatment of low-risk FN patients to be an effective and cost-effective strategy compared with continued in-patient hospitalisation. What does this paper add? This study demonstrates the sustainability of the ambulatory program in ensuring cost benefits and in-patient beds through real-life implementation data. It also provides evidence of the substantial cost and bed-days potentially averted when the cost savings and difference in LOS are estimated on a national scale over a 10-year time horizon. What are the implications for practitioners? The management of low-risk FN patients through ambulatory or out-patient programs is a safe and effective approach. There is strong evidence demonstrating the likely cost savings and considerable bed-days saved, which can be reallocated to meet other medical demands.