The aim of the study was to identify prognostic factors for weight loss in patients recently diagnosed with mild Alzheimer disease (AD), with special emphasis on the patients' social participation and living arrangements. The data used in this study was part of the Danish Alzheimer Intervention StudY. The patients were home-living patients with a clinical diagnosis, within the past 12 months, of probable AD or mixed AD; age =50 years; mini-mental state examination score =20; informed consent; and data available at 1-year follow-up. In total, 268 patients were included. We used a cut off of 4% in 1 year for defining weight loss. The mean age at inclusion was 76.1 years. Sixty-six patients (24.6%) lost more than 4% of their body weight during the study period. A logistic regression showed that an increase of 1 baseline body mass index point significantly increased the odds of weight loss by 9%. Furthermore, the results suggested a trend that for men, living alone was a risk factor for losing weight, whereas for women living with somebody was associated with a higher risk. However, further studies are pertinent within this area. As weight loss is a predictor of mortality in patients with AD, clinicians should be aware of prognostic social indicators to prevent or halt a potential negative development.