<b><i>Background:</i></b> Acquired deficiency of C1 inhibitor (AAE-C1-INH) is a very rare cause of recurrent angioedema, with few cases reported in the literature. We aimed to describe a series of patients with AAE-C1-INH who were diagnosed and received care at angioedema reference centers in Brazil, affiliated to the Brazilian Group of Studies on Hereditary Angioedema. <b><i>Methods:</i></b> Fourteen patients from 8 Brazilian Angioedema Reference Centers, diagnosed with AAE-C1-INH, were included in this study. Clinical data collected included sex, date of birth, date of onset of symptoms, date of diagnosis, plasma levels of antigenic and/or functional C1-INH, levels of C4 and C1q, location and treatment of angioedema attacks, long-term prophylaxis, associated diseases, and definitive treatment. <b><i>Results:</i></b> Fourteen patients were identified with AAE-C1-INH. Most patients (10/14; 71.4%) were female. The median age at onset of symptoms was 56.5 years (range, 14–74 years; interquartile range [IQR], 32–64 years), and median age at diagnosis was 58.0 years (range, 20–76 years; IQR, 38–65 years), with a median time until diagnosis of 2 years (range, 0–6 years; IQR, 1–3 years). The most common manifestations were cutaneous (face, eyelids, lips, trunk, hands, feet, and genitals). Most patient had low levels of C4 (13/14; 92.8%) and of antigenic C1-INH (8/14; 57.1%). Four had decreased functional activity of C1-INH (4/7; 57.1%) and C1q levels were low in 5 patients (5/12; 41.6%). Underlying diseases were identified in all 14 patients, with lymphoma of the splenic marginal zone and monoclonal gammopathy of undetermined significance being the most frequent. Nine patients (64.2%) needed long-term prophylactic treatment for recurrent angioedema and 5 patients (46.7%) required treatment for angioedema attacks. Most of them (12/14; 85.7%) had resolution of angioedema. <b><i>Conclusion:</i></b> Therapy of AAE-C1-INH aims to control symptoms; however, diagnosis and treatment of the underlying disease, when present, should be an important target and may lead to the resolution of angioedema in patients with AAE-C1-INH.
