Although dementia and nutritional status have been shown to be strongly associated, differences in body composition (BC) among older people with dementia have not yet been firmly established. The aim of this study was to assess BC through conventional and vector bioimpedance analysis (BIA and BIVA, respectively) in a sample of institutionalized older men with and without dementia, in order to detect dementia-related BC changes.Forty-one institutionalized men ages ≥ 65 y (23 without dementia [CG] and 18 with dementia [DG]) were measured with BIA and interpreted with BIVA and predictive equations.Age (74.4 and 75.7 y) and body mass index (22.5 and 23.6 kg/m(2)) were similar for DG and CG, respectively. Resistance and ratio of resistance to height did not differ significantly between the two groups. Reactance and ratio of reactance to height were 21.2% and 20.4% lower in DG than in CG. Phase angle was significantly lower in DG (mean = 4.0; 95% confidence interval [CI], 3.6°-4.3°) than in CG (mean = 4.7; 95% CI, 4.3°-5.1°). Mean fat mass index (6 and 7 kg/m(2)), and mean fat-free mass index (16.4 and 16.6 kg/m(2)) were similar in both groups. BIVA showed a significant downward migration of the ellipse in DG with respect to CG (T(2) = 15.1; P < 0.01).Conventional BIA showed no significant differences in BC between DG and CG, although reactance and ratio of reactance to height were about 21% lower in DG. Nevertheless, a body cell mass depletion and an increase in the ratio of extracellular to intracellular water were identified in DG using BIVA. BIVA reflects dementia-related changes in BC better than BIA.