Abstract: Background: Delirium is a syndrome characterized by an acute change in attention, awareness and cognition is caused by a medical condition that cannot be better explained by a pre-existing neurocognitive disorder. Delirium is a frequent complication in patients admitted to intensive cardiac care units (ICCU) with potentially severe consequences including increased risks of mortality, cognitive impairment and dependence at discharge, and longer times on mechanical ventilation and hospital stay. Aim of the study: To assess incidence and risk factors of delirium post primary percutaneous coronary intervention. Setting: the study was done in the coronary care unit at Assiut University Heart Hospital. Study design :descriptive research design used in the present study. This sample includes 60 patients. Tools: Three tools were used for data collection, Tool I: patient assessment questioner, Tool II: Assessment of delirium risk factor tool III: Assessment of delirium scale Results: the result showed that incidence of delirium was 83% and revealed that more than half of patients were aged above 50 years and more than two thirds of the patients were male, more than half of patients were smoking , more than two thirds of the patients were respiratory acidosis and hyperkalemia , near to half were discharged to home, more than one third were transferred to department and less than one third was died. Conclusion: The present study concluded that incidence of delirium among patients under study was 83%. and the most associated risk factors for development among patients were advanced age, smoking, respiratory acidosis, electrolyte imbalance, chest pain, hypoxia and respiratory infection. Recommendations: It recommended to continuously assess patients for delirium risk factors in order to develop delirium preventive measures, which influence patients outcomes and patient with delirium after primary percutaneous coronary intervention should have a great attention from nurses' staff to prevent risks as bleeding , hematoma.