Hyponatremia is the commonest electrolyte abnormality in hospitalized patients and occurs due to various causes. Here we present a case of SIADH who was diagnosed using commonly available biochemical tests. This case report also discusses the interaction of the laboratory physician with the treating clinician and the approach needed to arrive at a correct diagnosis. It highlights the importance of serum uric acid and fractional excretion of urinary uric acid in the diagnosis of SIADH. It also discusses the approach needed to distinguish SIADH from Cerebral Salt wasting syndrome, where the presenting feature is also hyponatremia.