Objective: To estimate the potential improvement in acute and rehabilitation hospital length of stay for rehabilitation patients from hypothetical scenarios that address barriers to patient flow. Design: Data about the duration of key processes for patients (n = 360) admitted to acute hospitals and subsequently transferred to inpatient rehabilitation in 2 wards in Melbourne, Australia were used to develop a computer simulation model. Subjects: Simulated patients. Methods: A computer model of length of stay was developed, validation checks performed and alternate care pathways simulated. Results: Almost all scenarios resulted in significant changes in the length of stay compared with baseline. The effect size for the changes was typically small to medium. The duration of the rehabilitation discharge barriers showed significant changes in all hypothetical scenarios. The effect size was smaller when changes were made to a single barrier, but larger when multiple barriers were changed simultaneously. Conclusion: Health system modelling can provide information regarding potential improvements in length of stay from addressing barriers to patient flow affecting rehabilitation patients. This can inform reforms to models of care and assist with cost benefit analyses. ? 2015 The Authors.