A patient with two attacks of glottis angioedema in a 15-day period without any apparent stimulus was studied. The complement profile of the patient revealed depletion of C4, C2, C1 inhibitor (C1INH) and C1q, with normal values of C3. Patient's offspring had a normal complement profile. Cytofluorographic analysis of the peripheral blood cells showed a marked increase of B cells. In the clotting study, a circulating lupus-like anticoagulant activity (LLA) was detected with a noticeable decrease of prothrombin time. Hepatosplenomegaly was confirmed by abdominal echography and CAT. From the liver biopsy it was concluded to be a lymphoproliferative process compatible with germinal center lymphoma. It is suggested that the neoplasm is probably the origin of the LLA and the cause of C1 activation, producing the biochemical defect of C1INH and the clinical symptoms of angioedema.