A young woman presented a severe gingivitis that wouldn't respond to antibiotics prescribed by her general practitioner. Thorough clinical examination showed atypical gingival inflammation. In such unusual cases a careful anamnesis is essential in determining appropriate continued diagnostic procedures. Eventually, acute myeloid leukaemia was diagnosed. Since the diagnosis of gingival disease primarily lies with the dentist, it is important to be able to consider any unusual aspects of gingivitis within a dental office.