Objective: To validate the QUALIDEM, a quality of life measure for people with dementia within residential settings rated by professional caregivers. Method: In a sample of 202 residents of nursing homes Spearman rank correlations were calculated between the QUALIDEM subscales aand indices of convergent validity and discriminant validity, with dementia severity and need of care, with global QOL scores by the head nurse and family, and with self-report on COOP/WONCA Charts. Results: The one-method multi-trait matrix showed 90.5% of the correlations to be in support for convergent and discriminant validity. Low to moderate correlations were observed with dementia severity and need of care, confirming that QOL is not merely disease severity. Support for concurrent validity was found in correlations with QOL ratings by the head nurse. The QUALIDEM did not correlate with most of the family ratings or with the COOP/WONCA Charts. Conclusion: The results of this validation study together with the obtained content validity through the method of construction provide sufficient support for validity of the QUALIDEM to be used for care evaluation and research in residential settings.