A rare hereditary angioedema characterized by potentially life-threatening episodes of subcutaneous and/or submucosal edema without urticaria and with normal levels and function of C1 esterase inhibitor. Patients present with prolonged attacks which last for approximately two to five days and may include nonpitting edema of the skin, severe abdominal symptoms such as pain and swelling, and/or respiratory distress due to upper respiratory airways involvement. Affected locations and frequency of attacks differ slightly between subtypes. Estrogen-containing oral contraceptives and pregnancy are precipitating factors, especially in patients with a factor XII mutation.