Cognitive stimulation is a psychological intervention widely used in dementia care, which offers a range of activities for people with dementia and provides general stimulation of cognitive abilities. This systematic review evaluates the effectiveness of cognitive stimulation in dementia. The review included studies from the Specialized Register of the Cochrane Dementia and Cognitive Improvement Group, called ALOIS. This yielded ninety-four studies, of which fifteen were randomised controlled trials meeting the inclusion criteria. The analysis included 718 subjects (407 receiving cognitive stimulation and 311 in control groups). Results were subjected to a meta-analysis. A consistent significant benefit to cognitive function was identified following treatment and the benefits appeared to be over and above any medication effects. This remained evident at follow-up up to three months after the end of treatment. In secondary analyses, with smaller total sample sizes, significant benefits were also noted for quality of life and well-being, and on staff ratings of communication and social interaction. No differences in relation to mood, activities of daily living or challenging behaviour were noted. There is consistent evidence that cognitive stimulation interventions benefit cognitive function and aspects of well-being. Cognitive stimulation should be made more widely available in dementia care.