A 65-year-old woman, referred to the endocrine clinic for investigation of tiredness and arthritis, was diagnosed as having diabetes on the basis of a positive family history and a raised glycated haemoglobin (HbA1) measurement. Subsequently, she was shown not to have diabetes but to have a persistently raised haemoglobin F (HbF) level. Initial assessment of HbF level by electroendosmosis demonstrated a normal HbF level but high values were confirmed using HPLC. Thalassaemia was excluded following DNA analysis. This case illustrates the importance of a glucose tolerance test following WHO criteria for the diagnosis of diabetes and emphasises that HbA1 is not a diagnostic test for diabetes.