 This study examined the relationship between emergency department length of stay, idlos, and in hospital mortality, IHM, and older patients. It found that idlos and boarding time, BT, are both associated with IHM, with a higher risk of IHM being observed in lower idlos and longer BT. Additionally, special attention should be paid to patients admitted after a short stay in the ED and a long BT, suggesting that these patients may benefit from more targeted interventions or dedicated teams to improve their outcomes.