The aim of this systematic review was to identify, assess and summarize studies about potentially inappropriate drug use (IDU) in cognitive impairment and dementia and to present findings about whether cognitive impairment and dementia are associated with IDU. The search was made in Medline/PubMed using free terms in the title or abstract. The inclusion criteria were: English language, published until 1 March 2014, original quantitative study and assessment of overall IDU with a consensus based summarized measure. Exclusion criteria were: focus on specific patient group (other than cognitive impairment or dementia), focus on specific drug class and failure to present a prevalence measure of IDU or an effect estimate (i.e. odds ratio). Of the initial 182 studies found in Medline, 22 articles fulfilled the criteria. Most studies used the Beers criteria for assessment of IDU. Prevalence of IDU among individuals with cognitive impairment or dementia ranged from 10.2% to 56.4% and was higher in nursing home settings than in community-dwelling samples. Most studies reported a lower likelihood of IDU in case of cognitive impairment or dementia. To conclude, IDU is highly prevalent among persons with cognitive impairment and dementia, although these conditions seem to be associated with a lower probability of IDU. This might reflect an awareness among clinicians of cautious prescribing to this vulnerable group of patients. More studies on large cohorts of persons with cognitive impairment and dementia are needed to draw conclusions about optimal drug prescribing to this frail group of older persons.