Acquired deficiency of C1 inhibitor (C1-INH) with angioedema symptoms (acquired angioedema, AAE) is characterized by local increase in vascular permeability (angioedema) of the skin and the gastrointestinal and oro-pharyngo-laryngeal mucosa. The mediator of symptoms is bradykinin, a potent vasoactive peptide, released from high molecular weight kininogen when it is cleaved by plasma kallikrein a serine protease controlled by C1-INH. Autoantibodies inactivating C1-INH are detected in the majority of patients and account for the deficiency. Irrespectively to the presence of anti-C1-INH autoantibodies lymphoproliferative diseases, ranging from benign monoclonal gammopathies to malignant lymphoma, are frequently associated with AAE. Demonstration that monoclonal components correspond to anti-C1-INH autoantibodies and correlation between course of lymphoma and course of AAE provide strong support to consider the two diseases expression of the same pathologic process.