Older adults represent an ever-growing proportion of the population of the industrialised nations, with a corresponding increase in the numbers of patients with dementing disorders. A common complaint in both normal aging and the dementias is that of significant sleep disturbance. The major causes of sleep disruption in aging and dementia include: (i) physiological changes that arise as part of normal, 'non- pathological' aging; (ii) sleep problems due to one of many physical or mental health conditions and their treatments; (iii) primary sleep disorders; (iv) poor 'sleep hygiene', that is, sleep-related practices and habits; and (v) some combination of these factors. Disrupted sleep in patients with dementia is a significant cause of stress for caregivers and frequently leads to institutionalisation of patients. It should be a target of clinical management when the goal is sustained home care, and when it is associated with disturbances of mood or behaviour. While the neuropathology of dementia can directly disrupt sleep, sleep disturbances in patients with dementia often have multiple causes that require systematic evaluation. Thorough assessment of associated psychopathology, day-time behaviour, medical disorders, medications, pain and environmental conditions is needed for optimal management. Differential diagnosis of a sleep problem in dementia is the basis of rational pharmacotherapy. However, patients with dementia are likely to be more sensitive than elderly persons without dementia to adverse cognitive and motor effects of drugs prescribed for sleep. Clinicians need to: (i) evaluate sleep outcomes when treating medical, psychiatric and behavioural disorders in older adults; (ii) be alert to emerging behavioural and environmental approaches to treatment; (iii) combine nonpharmacological strategies with drug therapies, when required, for added value; and (iv) avoid use of multiple psychotropic medications unless they prove essential to the adequate management of sleep disturbances.