Iron deficiency anaemia (IDA) is the most common form of anaemia worldwide. In men and postmenopausal women the commonest cause of IDA is blood loss from lesions in the gastrointestinal tract, making it a common cause of referral to gastroenterologists. Causes of IDA relate either to blood loss or iron malabsorption. After confirmation with laboratory tests, gastrointestinal evaluation is almost always indicated to exclude gastrointestinal malignancy. Specific patient groups such as premenopausal women, patients with low-normal ferritin and iron-deficient patients without anaemia may need an individualized approach. A small proportion of patients have recurrent or persistent IDA despite negative standard endoscopies. These patients with obscure gastrointestinal bleeding usually require evaluation of the small bowel with capsule endoscopy or double balloon enteroscopy. Treatment should involve prompt iron replacement plus diagnostic steps directed towards correcting the underlying cause of IDA. Oral iron replacement is cheap and effective, but parenteral (intravenous) therapy may be required due to intolerance, noncompliance or treatment failure with oral therapy.