BACKGROUND: C1-esterase inhibitor (C1eIn) is an important modulator of complement activation via the classical pathway. Deficiencies or dysfunction involving this inhibitor underlie the condition of angioneurotic oedema. AIM: The purpose of this report is to describe a female patient who presented at the age of 24 years with an apparently aggressive form of periodontitis and severe oedema, localised to the free gingival tissues. After 21 years of repeated surgical reduction of the gingiva, a diagnosis of C1eIn dysfunction was made. METHODS: Exhaustive serological investigations were performed along with histopathology. RESULTS: All investigations were unremarkable, until the function of the C1eIn molecule was investigated. These demonstrated a functional activity of only 29% and a raised C1q at 157 mg/l. Subsequent repeated investigation with careful specimen handling demonstrated undetectable levels of C1eIn and normal C1q. A diagnosis of C1eIn dysfunction was made, although at present it is unclear whether this represents an unusual variant of hereditary dysfunctional C1eIn deficiency. The patient was managed by various means, including steriodal and non-steroidal drugs, the latter forming part of her maintenance regime. CONCLUSIONS: To our knowledge, this is the first case of angio-oedema localised to the free gingiva. The role of stress in the acute exacerbations of oedema and bone loss is discussed along with the diagnostic pitfalls associated with this case.