Aim The aim of the present retrospective study was to investigate the time‐courses of the cognitive, behavioral and physical status of day care service users with dementia, and to determine the factors associated with the long‐term use of day care in order to aid the development of better interventions. Methods We analyzed the data of 162 consecutive patients who attended our day care clinic for 1 year or more between 1 April 2000 and 31 March 2010. The patients were divided into three groups according to the length of their day care attendance (the 1‐year, 3‐year and 5‐year groups). Then, we investigated the time‐courses of their cognitive, behavioral and physical status. Logistic regression analysis was used to detect the factors that affect the duration of day care service attendance in dementia patients. Results The Hasegawa Dementia Scale‐Revised (HDS‐R), Assessment Scale for Symptoms of Dementia (ASSD) and Nishimura's Activities of Daily Living (N‐ADL) scores of the three groups all significantly deteriorated during the study period except for the HDS‐R score of the 3‐year group. Higher age and a high ASSD score were associated with a short period of day care service attendance, whereas the patients' daughters‐in‐law acting as a caregiver was related to the long‐term use of day care services in model 1. Conclusions It is better to control behavioral and psychological symptoms in order to improve the utilities of day care for dementia patients. The caregiving environment of dementia patients might be associated with the length of day care attendance. Geriatr Gerontol Int 2013; ●●: ●●–●●.