It is important to evaluate body composition changes in subjects with an existing multi-system reduction in capacity, as a small decrease in fat-free mass (FFM) can cause serious impairments. The aim of the study was to describe body composition in old people living in institutions. Body composition data were collected within a study of 173 subjects with functional and cognitive impairment, aged 65-99 years, and living in residential care facilities. A bioelectrical impedance spectrometer (BIS) (Xitron Hydra 4200; 5-1000 kHz) was used to assess the amount of both FFM and fat mass (FM) which where adjusted for height. The Harpenden caliper and a tape measure were used to assess body fat, arm-muscle and arm-fat area (mm(2)). A large proportion of the old and functionally impaired population was at risk of malnutrition or already malnourished (63.4% vs. 17.4%) according to Mini-Nutritional Assessment (MNA). Women had significantly lower fat-free mass index (FFMI) and higher FMI, inversely related to age, than men. Bioelectrical impedance spectroscopy and anthropometrical measurements correlated but on different levels. In addition the FM% differed between the two methods (46.3% vs. 33.4%).