Physical exercise has positive effects on cognitive functioning in both healthy older adults and ambulatory older adults with dementia. The present study investigated whether a 10-week multimodal movement intervention conducted in the seated position can slow cognitive deterioration in demented and physically very frail nursing-home residents. Our analysis revealed that training participants showed no further overall cognitive deterioration throughout the study and a significant improvement in the ADAS-Cog orientation/praxis subscore (p = .04). In contrast, the control group demonstrated a significant decline in the ADAS-Cog sum score (p = .02). These results might be of relevance for geriatric practice since they indicate that a short-term physical intervention – even in the seated position – can decelerate cognitive decline and dementia despite physical frailty.