According to the reference values of the World Health Organization (WHO), anaemia is defined as a haemoglobin (Hb) level < 8.1 mmol/l in men and < 7.5 mmol/l in women. Lower reference values are often used in older patients because many doctors consider a decreased Hb level to be physiological in advanced age. However, Hb values under the WHO reference values are associated with increased mortality in older persons. Moreover, a cause of the anaemia is found in > 80% of older persons with anaemia if further diagnostic tests are done. Decreased Hb levels are also associated with functional impairments such as mobility disorders. These findings apply not only to severely decreased Hb levels but also to Hb levels that are only slightly below the WHO reference values. Correspondingly, increased erythropoietin levels are seen in older persons with severely decreased Hb levels as well as in older persons with slightly decreased Hb levels. Thus, a decrease in the Hb level in advanced age is not physiological and the WHO reference values for anaemia are also valid for older persons.