OBJECTIVE: The aim of this study was to establish the epidemiological features of agitation and aggressiveness in patients aged 65 years or older, living at home, whatever etiological factors might be, to found the cost analysis in the absence of published data. METHODS: Prevalence was estimated, first, in a random sample of 3777 elderly subjects (the “PAQUID” cohort), using DSM-III criteria and psychologists reports, at different timepoints; second, in the patients of a national representative sample of 159 general practitioners from diagnoses based on behaviors and clinical scrutiny. A national retrospective study including 410 patients was conducted to investigate the consequences of those symptoms, like somatic troubles, social disability and dependence. Disability was also evaluated in the “PAQUID” cohort with the “AGGIR” scale used to identify patients eligible to a “dependence specific benefit”. Risk factors (age, gender, medical variables…) were examined. RESULTS: In 1997, prevalence of agitation and aggressiveness ranged between 0.19 and 0.34% of French population. 55% of concerned subjects presented 2 to 3 somatic troubles, 97% a restriction of social life and 85% of daily activities. Prevalence depended positively on age. Men exhibited more symptoms than women (p<0.0001). Agitation and aggressiveness were mainly associated with demence and psychiatric diseases, but demented subjects showed more physical agitation (p<0.02), social disability and dependence (p<0.0001). CONCLUSION: The economic impact of agitated and aggressive behaviors of elderly individuals should be great due to the high degree of associated disability, and increase in the future.