It is well-known that subclinical and overt malnutrition are strong predictive indices of morbidity and mortality in old subjects, particularly in demented ones, and may deeply affect the quality of life. The aim of this study was evaluation of nutritional status in demented patients, as a whole and according to type of dementia, at the moment of hospital admission and before discharge. The study concerns 174 old demented patients, aged 80.2 +/- 8 SD, diagnosed as having Alzheimer's disease, vascular dementia, degenerative and vascular dementia, reversible dementia, and other types of dementia. In each subject, anthropometric measures, body composition analysis by the bioelectric impedance technique, Mini Nutritional Assessment (MNA) and cognitive, functional and affective assessment by conventional geriatric instruments were performed. A blood sample allowed assay of the main biochemical nutritional markers. At the end of the hospitalization period, the same cognitive, functional and nutritional assessment was repeated, in order to evaluate the effects of vitamin and protein supplements and of care during meals. In all subgroups of demented patients, obtained according to type of dementia, the mean MNA score was indicative of risk for malnutrition. Furthermore, the MNA score was significantly related to severe cognitive impairment, functional status, comorbidity, BMI values, and transferrin and total protein serum levels. Malnourished patients and demented elderly at risk for malnutrition (according to the MNA score) were given oral nutritional supplements during hospitalization, lasting a mean of 45 days. Before discharge, these two subtypes of demented patients showed substantial maintenance of their cognitive, functional and nutritional status, whereas the subgroup of well-nourished demented patients exhibited significant worsening of the nutritional pattern. Demented patients show a high percentage of malnutrition, particularly evident in subjects with deeper cognitive impairment. Nutritional status seems to be linked more to functional abilities than to duration of disease. However, nutritional intervention or special care during meals may act in synergy with specific pharmacologic therapy of dementia.