BACKGROUND: Summer 2003 witnessed an excess in heat-related mortality in the elderly population. The Argento Project was planned to define risk factors for heat-related death in Modena, Italy, during the hottest month of 2003 (August). METHODS: We performed a retrospective, case-control study of a cohort of 394 older persons living in Modena, 197 dead (cases) and 197 survivors (controls). A questionnaire to collect information about demographic, social, environmental, and clinical characteristics and about causes of death was completed. RESULTS: Cases were more likely to be living in a nursing home and needing assistance (p Euro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin).024, and p <.001, respectively). Survivors were living on higher level floors (p Euro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin).046). Spending the summer in Modena was significantly related to poor outcomes (p <.01). A higher number of cases were using public health services (p <.001). Individuals who died had a greater degree of comorbidity and dependence (p <.001); they were cognitively impaired (p <.001), took a larger number of drugs (p <.001), and had a greater number of hospital admissions (p <.001). Multivariate analysis showed that patients who spent the summer in Modena had a higher mortality. Other predictors of death were the use of home public-integrated assistance, a higher comorbidity and a higher degree of disability; the loss of at least 1 Activity of Daily Living (ADL) represents the strongest risk factor of heat-related death. CONCLUSIONS: Our study identifies the major risk factors of heat-related death in the elderly population. With the creation of an up-to-date database, when a new heat wave will come, it will be possible to identify frail persons for preventive targeted strategies.