OBJECTIVE : This study was designed to estimate the cost incurred by French Social Security due to agitated and aggressive behaviors of patients aged 65 years or older, living at home. METHODS : Economic appraisal was performed on a representative sample of 410 patients included by 212 general practitioners in a national specific retrospective survey. The bottom-up approach to calculating cost of those psychotic symptoms for total population was based on our preliminary estimation of their prevalence. The whole direct medical costs were taken into account so as the medical costs of dependence associated to behavior troubles. The main determinants of costs were examined through the various profiles of patients we pointed out. RESULTS : In 1997, the average cost for the French Social Security of an agitated and aggressive old patient dwelling in the community was estimated to 23,513 ± 1,665 FF. It varied with the age of patients, from 18,392 ± 2,642 FF in the 65-78 years old to 21,920 ± 3,447 FF in the 88-99 years old with a peak in the 79-87 years old patients (29,724 ± 2,675 FF) [p<0,01]. The average cost of demented patients (27,791 ± 2,239 FF) appeared to be significantly higher than non demented (18,410 ± 2,445 FF) [p<0,005]. Health care services at home for dependent patients were the most costly category of service. CONCLUSION : Our results highlighted the economic interest of better controlling those behavior disorders with special emphasis on demented patients in order to prevent them from becoming dependent.