Angiotensin-converting enzyme inhibitors (ACEIs) are used increasingly for the treatment of hypertension and chronic heart failure, and they reduce mortality when given after myocardial infarction. Of the patients prescribed these drugs 0.1-0.7% develop angio-oedema, but the association is not widely recognized. In 60% of cases the onset occurs during the first week of treatment; however, it may be considerably delayed. Angio-oedema nearly always occurs on the head and neck, frequently involving the mouth, tongue, pharynx and larynx. The course is unpredictable, and attacks vary in severity from mild to fatal from laryngeal obstruction. Severe ACEI-induced angio-oedema may require emergency treatment with adrenalin and early intubation. The drug should be withdrawn in any patient who presents with ACEI-induced angio-oedema, and treatment continued with an appropriate drug of a different class. Therapy with ACEIs is contraindicated in patients with a prior history of idiopathic angio-oedema, or in patients with hereditary or acquired C1 esterase inhibitor deficiency.