This paper describes a middle-aged patient who developed repeated episodes of swelling of the orofacial tissues after dental treatment. On investigation, C1 inhibitor, C1q, C2, and C4 levels were all markedly reduced, and a diagnosis of acquired C1 inhibitor deficiency was made. The patient had been diagnosed with non-Hodgkin's lymphoma (NHL) 2 years previously and had undergone a successful course of chemotherapy. The development of her episodes of angioedema prompted thorough reinvestigation and a recurrence of NHL was identified. Therefore, acquired C1 inhibitor deficiency heralded a recurrence, although this had not been a manifestation when NHL was first diagnosed. The patient underwent a further course of chemotherapy and remains well, although C1 inhibitor, C1q, C2, and C4 levels remain reduced.