Thyrotoxic crisis is a medical emergency with an associated mortality of 10-75%. It is usually encountered in patients with poorly controlled or undiagnosed Graves' disease. The occurrence of thyrotoxic crisis is rare due to routine function tests, which enable a diagnosis to be made even in its subclinical form. However, a thyrotoxic crisis can develop rapidly and bears little relationship to circulating thyroid hormone levels. We present a case of a thyrotoxic crisis in a 52-year-old woman, whose emergent thyroid function tests revealed a near normal euthyroid level. Her Hb A1c was 10.5% before the operation.