Abstract There is little research literature on patient flow in rehabilitation. Accepted definitions of barriers to discharge and agreed performance measures are needed to support research and understanding of this topic. The potential of improved patient flow in rehabilitation to assist relieving demand pressures in acute hospitals underscores its importance. This study develops a definition of barriers to discharge from postacute care and classifies their causes using a multiphased iterative consultation and feedback process involving physiatrists, aged-care physicians, and senior nursing and allied health clinicians. Key performance indicators (KPIs) for postacute patient flow are then proposed, the development of which were informed by the available literature and a survey (n=101) of physiatrists, aged-care physicians, and hospital managers with responsibility for patient flow who were questioned about the use of relevant KPIs in this setting. Most (>70%) respondents believed that using KPIs (eg, waiting time from acceptance by postacute care and ready for transfer until admission, percentage of postacute bed days occupied by inpatients with a discharge barrier) to measure aspects of patient flow could improve processes, but few reported collecting this information (45% admission KPIs, 19% discharge KPIs). By using the definition and classification of discharge barriers prospectively to document and address barriers, in conjunction with appropriate KPIs, postacute patient flow and the efficiency of hospital resource utilization can potentially be improved. Our commentary aims to stimulate interest among others to develop a more robust evidence base for improved flow through postacute care.