A 22-year-old Chinese woman presented with typical features of diabetic ketoacidosis. There was a family history of diabetes but she was not obese. Plasma glucose and bicarbonate levels were 27.0 mmol/l and 5 mmol/l, respectively. Significant insulin resistance was noticed: she needed up to 15 units of insulin per hour. She required up to 120 units daily for her diabetic control even after her acidosis had subsided. She was then noticed to have the clinical features of acromegaly. The diagnosis was confirmed, and a cranial CT scan confirmed the presence of a pituitary macroadenoma. She underwent uneventful trans-sphenoidal resection of the tumour and her insulin requirement gradually lessened. Acromegaly should be considered in the differential diagnosis of unexplained insulin resistance.