Cognitive rehabilitation (CR) is a promising treatment approach for older adults with dementia because it aims at supporting the management of day-to-day problems. There is insufficient evidence regarding whether CR provides clinically meaningful benefits. In this study, we evaluated the feasibility, acceptance, efficacy, and usefulness of a CR intervention in a multicenter, randomized, controlled trial on 201 patients with mild dementia in Alzheimer disease and their carers. The intervention comprised 12 individual weekly sessions and combined 4 established strategies adopted from neurorehabilitation and psychotherapy. Activities of daily living were chosen as the primary outcome. The results show that the feasibility, treatment adherence, and carer commitment were excellent. However, no effect of the intervention was demonstrable on everyday functioning. There were improvements favoring the intervention on quality of life and treatment satisfaction and a significant antidepressant effect in female participants. The lack of impact on everyday activities may be due to methodological limitations including insufficient personalization, short treatment duration, poor transfer into the real-life setting, and low sensitivity of assessment instruments. The findings of this study may be helpful for designing further studies that are needed to determine the potential of CR in older adults with dementia.