Diabetes insipidus is a syndrome characterized by hypotonic polyuria: 24-h urine volume >50 mL/kg under conditions of ad lib intake; urine S.G. <1.010; absence of solute diuresis (dipstick negative for glucose). Failure to meet any of the criteria given above renders further evaluation unnecessary. Disorders of inappropriately decreased AVP or AVP effect: central diabetes insipidus; nephrogenic diabetes insipidus; primary polydipsia; gestational diabetes insipidus; osmoreceptor dysfunction. Diabetes insipidus with an intrasellar lesion: metastatic tumor (lung, breast, lymphoma); pituitary apoplexy; rapidly enlarging pituitary tumor and pituitary abscess. Evaluation and follow-up of a thickened pituitary stalk with CDI: blood and CSF ACE, AFP and β-hCG levels; CSF cytology ± flow cytometry, AFB culture; CXR/chest CT; bone survey. If all are negative, repeat MRI every 6 months for 2 years and then yearly for 1-3 years; assess anterior pituitary function yearly; if stalk thickening persists, repeat CXR and bone survey yearly; consider biopsy of pituitary stalk if thickening exceeds 6.5 mm at any time.