Background:Young-onset dementia (YOD) has a profound impact on spouses. However, little is known on how the quality of the relationship changes over time in YOD. This study aims to determine how the quality of the relationship changes over time and identify predictors of this change.Methods:This study used data from the NEEDs in Young onset Dementia (NeedYD) study. The primary outcome measure was the quality of the relationship perceived by spouses measured throughout 24 months. Baseline characteristics of persons with YOD and spouses were also measured to assess their predictive value.Results:Totally, 178 dyads were included. The perceived quality of the relationship deteriorated over time. A longer symptom duration, a diagnosis of frontotemporal dementia, lower levels of awareness of deficits, lower levels of initiative toward daily living activities, and higher levels of apathy, hyperactivity, depression, and anxiety in the person with YOD were associated with a lower perceived quality of the relationship by spouses. A coping style characterized by palliative and passive reacting patterns and higher levels of neuroticism in spouses was also associated with a lower quality of the relationship.Conclusion:The quality of the relationship as perceived by spouses deteriorated over time and was influenced by characteristics of the person with YOD as well as their spouse. Helping spouses to come to terms with factors that threaten their sense of couplehood might help them to develop a more positive attitude toward their spousal relationship and improve the quality of the relationship and care.