Type 1 hereditary angioedema (HAE) is a rare genetic condition characterized by recurrent episodes of oedema caused by a deficiency of C1-esterase inhibitor (C1-INH). A 29-year-old male presented to the oral medicine department at Guy’s Hospital, London, with lip swelling following crown preparation and impressions. Haematological investigations showed reduced levels of complement C4 (0.02 g/L; reference range 0.1–0.4 g/L) and C1-INH function was <31% (reference range 85–99%). Immunology confirmed the diagnosis of type 1 HAE, with a de novo mutation. This case highlights how a detailed medical history and multidisciplinary teamwork ensure the correct diagnosis and management. CPD/Clinical Relevance: To demonstrate the various dental triggers, relevant signs and symptoms, and management options for patients diagnosed with hereditary angioedema to allow for effective decision-making in a primary dental setting.