Drugs are a frequently cited cause of dementia. There is a paucity of data regarding the incidence of drug-induced dementia, but it has been estimated that over 10% of patients attending memory clinics have iatrogenic disease. Drugs may impair cognition indirectly via metabolic effects, such as hypoglycaemia, by alterations of immunological factors within the CNS, and by actions that interfere with synaptic transmission. Classes of drugs most frequently responsible are the benzodiazepines, antihypertensives and drugs with anticholinergic properties. Each of these classes is likely to produce a different pattern of neuropsychological deficits. Prevention of drug-induced dementia will be aided by: (i) minimising the number of drugs prescribed; (ii) using shorter-acting preparations; (iii) avoiding agents that cross the blood-brain barrier where possible; (iv) evaluating renal and hepatic function regularly; and (v) briefly assessing cognitive function before treatment.