Objective: Delirium superimposed on dementia (DSD) is common and associated with adverse outcomes. Current evidence indicates that some patients with dementia may recall delirium with distress for them and their caregivers. The aim of this study is to identify predictors of distress in informal caregivers of older patient with DSD.; Methods: A total of 33 caregivers of 33 patients with DSD were interviewed 3 days after the resolution of delirium (T0) and at 1-month follow-up (T1) to describe their level of distress related to the delirium episode. A linear regression was used to identify predictors of caregivers' distress at T0 and T1 defined a priori: age, sex, level of education, employment status, delirium subtypes, delirium severity, type and severity of dementia, and the time spent with the patient during the delirium episode.; Results: Caregivers were mostly female (81%), 59 (± 13.0) years old on average. The predictors of distress at T0 were the patient's severity of both dementia and delirium. Moderate dementia was associated with lower distress, whereas higher delirium severity was associated with greater distress. At 1-month follow-up, the predictors of distress were the age of caregiver and time spent in care; the distress level was higher when caregivers were older, and they spent less time with their loved one.; Conclusions: These preliminary findings underline the importance of providing continuous training and support for the caregivers, especially in coping strategies, in order to improve the care of DSD patients and prevent the caregivers' distress in long time period.