Which condition is caused by a deficiency of antidiuretic hormone (ADH) in the body?

Diabetes insipidus is indeed the condition caused by a deficiency of antidiuretic hormone (ADH), also known as vasopressin. This hormone is critical for regulating water retention in the kidneys. When there is insufficient ADH, the kidneys cannot reabsorb water effectively, leading to excessive urine production (polyuria) and increased thirst (polydipsia).

In contrast, diabetes mellitus is primarily associated with insulin deficiency or resistance, which affects glucose metabolism rather than water balance. Hypothyroidism relates to a deficiency in thyroid hormones affecting metabolism and energy levels, while Addison's disease results from a lack of adrenal hormones, typically cortisol and aldosterone, which also does not involve ADH. Thus, the distinctive role of ADH in managing water balance makes diabetes insipidus the correct answer in this context.