Hereditary angioedema (HA) is caused by a quantitative or qualitative deficiency of C1 esterase inhibitor (C1 INH). We present a study of nine patients with HA belonging to two different families. The symptoms started before 10 years of age in most cases (78%). Facial edema (lips, eyes) and of the extremities (feet, hands) were the most frequent complaints. Three patients presented edema of the glottis and one of them underwent a tracheostomy twice. Laboratory tests, outside the acute crisis, revealed low levels of C4 in all patients. The serum levels of C1 INH were normal in seven patients; however, functional activity was not observed in any of them. After the use of a modified androgen (danazol), control of symptoms was observed in all patients, although functional activity was re-established in only five patients.