Objectives: In clinical settings, untreatable biliary sludge in the gallbladder can be observed in older adults with advanced dementia. The underlying cause of biliary sludge existence in patients with dementia is currently unknown. Therefore, we aimed to investigate the prevalence, risk factors, and related outcomes of biliary sludge formation in the gallbladder of older adults with dementia Design: Cross-sectional study. Setting: Geriatric ward of University Hospital in Japan Participants: Inpatients aged 80 and older suffering with dementia. Measurements: We evaluated the presence of biliary sludge by diagnostic ultrasonography and collected data regarding patient demographic information, cognition (mini-mental state examination [MMSE]), physical activity (Barthel Index), oral food intake (food intake level scale [FILS]), clinical stage of dementia (functional assessment staging [FAST] of dementia), and patient performance status (Zubrod/ Karnofsky score). Results: Male sex, larger gallbladder volume and calories from oral intake were significantly associated with the presence of biliary sludge (P =.02, .02, .002, respectively). There was a significant negative correlation between the FAST stage and the FILS level in all patients (P <.001). More advanced dementia and dysphagia was more likely to be found in patients with Alzheimer disease (AD) with biliary sludge, compared to patients with AD without biliary sludge (FAST 7a, FILS II and FAST 6c, FILS V, respectively, P =.06, 04). A logistic regression analysis revealed that the eating status of FILS I and II, generally called “fasting or anorexia”, was a significant risk factor for forming biliary sludge in older adults with dementia (P =.031, odds ratio: 5.25, 95% confidence interval: 1.16-23.72). Conclusions: Fasting status may be associated with the existence of biliary sludge in older adults with dementia. Therefore, supportive care for eating might be an important solution to comfortable end-of-life care for older adults with advanced dementia.