To study longitudinal changes in the quality of life (QoL) in persons with and without dementia, and explore the factors associated with baseline QoL and changes of QoL over the follow-up period.

Prospective longitudinal study.

Data were collected from 17 municipalities in Norway in the period from January 2009 to August 2012. A total of 412 persons were included, 254 (61.7 %) persons without dementia and 158 (38.3 %) with dementia at baseline.

Persons 70 years of age or older, receiving municipal care services. Main outcome measures include the following: self-rated and proxy-rated QoL over a period of 18 months, cognitive status, functional status, neuropsychiatric symptoms, and demographics.

Longitudinal changes in QoL were small, despite changes in clinical variables. Proxy ratings of patients QoL were lower than the patients’ own ratings. Belonging to a group with low QoL trajectory was associated with symptoms of depression, reduced physical and instrumental functioning, and more severe dementia.

Patients and proxies evaluated the patients’ QoL differently and QoL did not necessarily correspond with deterioration in clinical parameters. To prevent impaired QoL, we need to address identified factors and keep an approach open to the individual perceptions of QoL.