BACKGROUND: Underweight and weight loss are important factors in detecting malnutrition. OBJECTIVE: To describe underweight, weight loss and related nutritional factors after 12 months among individuals 75 years or older and living in sheltered housing. A further aim was to identify possible risk factors associated with underweight and weight loss. DESIGN: This is a part of a cross-sectional follow-up study from a county in Sweden, examining the disabilities, resources and needs of 719 older adults in sheltered housing units. Data were collected twice, with a 12-month interval using the Resident Assessment Instrument. RESULTS: Among the 503 remaining chronically ill individuals with cognitive and functional disabilities, 35% were classified as underweight at the initial assessment and 38% at the second, a non-significant difference. A further analysis showed 39% had decreased weight, 27% remained stable and 28% gained weight. A weight loss of 5% occurred in 27% of the older adults and a loss of 10% occurred in 14%. Risk factors associated with being underweight and weight loss, using scales derived from the instrument were cognitive and functional decline. Dementia and Parkinson's disease, eating dependencies and constipation were the strongest risk factors when analyzed as single items. CONCLUSION: A high percentage was underweight or exhibited weight loss and several risk factors were identified. Ensuring adequate nutritional status in individuals with a variety of diseases and declining health status is challenging. Increased combined efforts using a wide range of measures, nutritional programs and routines need to be regularly implemented.