Purpose: This study explored whether adult day service (ADS) use was associated with reductions in behavioral and psychological symptoms of dementia (BPSD) in individuals with dementia. Design and Methods: We used a quasi-experimental design to compare a group of 133 persons with dementia (PWDs) who initially enrolled in an ADS program to a control group not using these services (n = 68). Caregivers used a 24-hour log on multiple, consecutive days to report on five domains of BPSD. Results: We used growth-mixture modeling techniques to model change in the BPSD domains over a 2-month period as well as to handle the preponderance of zeros that were inherent in the data. Results showed a relationship between ADS use and caregivers' report of fewer nighttime sleep-related problems for their PWDs. We found trends for other domains, specifically depressive symptoms and agitated behavior, but no significant group differences emerged for these and the other domains. Implications: The findings of ADS use on PWDs' duration of nighttime sleep problems provide some evidence of the benefits of ADS; the findings also support its utility as part of the continuum of care for PWDs and their caregivers. For other behavior domains, enhanced or more targeted behavioral strategies coupled with ADS might offer caregivers and their PWDs the best possible combination for ameliorating BPSD. (Contains 3 footnotes, 4 tables, and 2 figures.)