Isolated angioedema may be the presenting symptom of acquired C1 inhibitor (C1-INH) deficiency. C1-INH deficiency is associated with lymphoproliferative disorders. Treatment of the underlying disease can result in a complete reversal of clinical and complement abnormalities. We describe a 41-year-old woman who was referred to our emergency department with recurrent episodes of isolated angioedema. Initially, her angioedema was linked to the use of angiotensin receptor blockers. However, after discontinuation of this drug angioedema recurred. Additional investigations revealed the presence of acquired C1-INH deficiency caused by an indolent non-Hodgkin's lymphoma. Treatment with rituximab resulted in complete clinical and biochemical remission of the acquired angioedema.