Objectives: To characterize body weight and nutritional status of a cohort of elderly nursing home residents in Adelaide, South-Australia, and the factors associated with changes in these measures over 6-12 months. Design: Retrospective study. Setting: Nursing homes affiliated with a single provider of aged care. Participants: Residents aged 87±8years. Measurements: Age, gender, body weight and body mass index (BMI), pain, length of stay, and nutritional status assessed by malnutrition universal screening tool (MUST), were obtained from a data base. Changes in these parameters over 6 to 12 months were determined, as were factors associated with weight change. Results: 1,020 residents were in the 6-months retrospective analysis, and a subset of 752 residents in the 12-months sub-group. The average weight and BMI for the overall cohort were 66±16kg and 25±6kg/m2. Almost 30% of residents were at medium or high nutritional risk (14% and 16%). Body weight decreased 0.4±4.1kg (0.5±6.4%) over 6-months (P=0.006) and 0.9±5.2kg (1.3±7.8%) over 12-months (P<0.001). 46% of residents had marked weight change (≥ 5% loss or gain) over 12-months. Residents in the lowest BMI tertile (≤23kg/m2) were most likely to experience both marked weight change (52%) and weight reduction (30%). Weight loss was associated with higher pain scores (P=0.012) and greater length of stay in the nursing home (P=0.002). Conclusion: On average these older people lost weight, with high rates of both substantial weight loss and gain, particularly among those in the lowest BMI tertile. Almost a third in the lowest BMI tertile lost 5% or more body weight, putting them at increased risk of undernurition-related morbidity, suggesting greatest attention to prevent and treat such morbidity should be focused on that group.