Rationale: Angioedema (AE) without urticaria is idiopathic in the majority of cases. We studied patients with AE by genetic analysis for novel mutations of proteins interacting with the bradykinin pathway. Methods: 126 patients with AE were recruited at a university hospital clinic. Patients were categorized according the proposed pathogenesis of AE: C1 inhibitor deficiency and low C4 levels, autoimmune disease, malignant cancer, angiotensin-converting enzyme (ACE) inhibitor-induced, nonsteroidal anti-inflammatory drug (NSAID)-induced, or idiopathic. In addition, each patient had a blood sample analyzed for a complement profile and enzymes (antigenic and functional C1 inhibitor, C3, C4, CH 50), and immunologic parameters. A subset of 52 patients was tested for specific mutations in factor XII, plasminogen-activator inhibitor-1 (PAI-1), ACE, and aminopeptidase P (APP). Results: The cause of angioedema was identified in 52 (41%) of the cases: 3 (2%) patients had a low plasma C1 inhibitor and C4; 18 (14%) were ACE inhibitor-induced; 10 (8%) were due to autoimmune disorders; 5 (4%) were associated with malignancy; and 16 (13%) were due to NSAIDs. In the remaining 74 (59%) patients the cause of angioedema was idiopathic. In those with genetic analysis 13 (25%) had a specific genetic variant in APP, 10 (19%) in ACE, 13 (25%) in PAI, and 0 in Factor XII. Conclusions: In addition to related diseases and medications causing AE, certain genetic variants encoding proteins in the bradykinin generation and/or catabolism pathways may be implicit in the pathogenesis of AE. Further studies are ongoing.