Epidemiological studies suggest that anxiety and depression are less common in older than younger adults. One in ten people aged > or = 65 fulfils the diagnostic criteria for at least one common mental disorder. Older depressed patients have an increased risk of both cardiac and all-cause mortality. Both anxiety and depression in older patients are often unrecognised and untreated, and have a poor prognosis. There is a progressive decline in the prevalence of common mental disorders above the age of 55. Anxiety and depression often occur together, and share many risk factors. However, anxiety tends to follow threats or traumatic events, whereas depression follows loss events. Chronic diseases, cognitive impairment, pain and functional disability are risk factors for the onset of depression, but not anxiety. Depression is between two and three times more common among those with a chronic physical health problem. Even patients with major depression often remain unrecognised and untreated. Generalised anxiety disorder (GAD) is by far the most common anxiety disorder in older people but most GAD patients are not recognised in primary care and only a third of them receive any form of treatment. Older patients often deny feeling anxious or depressed and are more likely to present with insomnia, irritability, agitation and multiple somatic complaints. GPs may erroneously believe that depression is a normal reaction to the losses of old age, and may be reluctant to initiate treatment. A good case can be made for replacing the PHQ-9 with the 15-item version of the Geriatric Depression Scale which almost entirely avoids somatic questions. This is a screening not a diagnostic tool and does not evaluate symptom severity.