Hereditary angioedema is a rare disease, transmitted as an autosomal dominant trait. The disease usually manifests as acute subcutaneous or submucosal swellings and abdominal pain of two to five days duration. When localized to head or throat, life-threatening edema of the larynx may occur. The disease is caused by reduced amount of active C1 inhibitor. The edema is not due to an allergic reaction and medication for such is of little or no value. Prophylactic medication may be given when the attacks are frequent and ought to be given before dental extractions, intubation of the larynx, major surgery especially of the oro-pharynx, and birth. An acute attack is best treated by intravenous injection of C1 inhibitor concentrate.