Diabetes insipidus is a condition in which the body cannot retain enough water. The patient is excessively thirsty and excretes large amounts of extremely diluted urine - a reduction in fluid intake does not reduce amounts and consistency of urine excretion. It is a rare condition, affecting approximately 1 in every 25,000 people. 

Diabetes insipidus is not related to diabetes mellitus (sugar diabetes). The term diabetes on its own nearly always refers to diabetes mellitus. This article is about diabetes insipidus - the condition characterized by intense thirst and polyuria (excretion of large amounts of urine). 

In most cases diabetes insipidus occurs because the body does not properly produce, store or release a key hormone - arginine vasopressin (AVP), also known as antidiuretic hormone (ADH). It may also occur when the kidneys do not respond properly to ADH (antidiuretic hormone). 

There are three types of diabetes insipidus:

Neurogenic diabetes insipidus - a deficiency with ADH (antidiuretic hormone).

Nephrogenic diabetes insipidus - insensitivity of the kidneys to ADH.

Gestational diabetes insipidus - in very rare cases diabetes insipidus may also occur during pregnancy.

According to Medilexicon's medical dictionary:

Diabetes insipidus is "Chronic excretion of very large amounts of pale urine of low specific gravity, causing dehydration and extreme thirst; ordinarily results from inadequate output of pituitary antidiuretic hormone; the urine abnormalities may be mimicked as a result of excessive fluid intake, as in psychogenic polydipsia. Two types exist: central and nephrogenic. Autosomal dominant [MIM*125700, *125800, *192340], X-linked [MIM*304800 and *304900], and even autosomal recessive forms [MIM*222000] have been described."