Background Affective disorders are associated with cognitive disturbances but their role as risk factors for dementia is still not fully investigated. Aims To evaluate the risk of developing dementia in individuals with a history of affective disorder. Method We conducted a systematic review of case control and cohort studies addressing the risk of developing dementia in people with affective disorders. To the best of our knowledge, this is the first systematic review that has included studies evaluating this risk specifically in people with bipolar disorder. Results Fifty-one studies were included. Most of the studies found an increased risk for developing dementia in individuals with depression. Greater frequency and severity of depressive episodes seem to increase this risk. The evidence is contradictory regarding whether there is a difference in risk in people with early- or late-onset depression. The few available risk estimates for dementia in people with bipolar disorder suggest an even higher risk than for those with depression. Conclusions Affective disorders appear to be associated with an increased risk of developing dementia, and one that is dependent on clinical and demographic variables. Depression may be both a prodrome and a risk factor for dementia. Future research should aim to elucidate the mechanisms that mediate these links.