Lucky, a 5-year-old female, spayed domestic shorthair cat was referred to the Cornell Internal Medicine Service on February 8th, 2007 for a six-month history of intermittent dehydration and secondary chronic hypernatremia due to adipsia. Lucky had no previous medical history except a non-clinical grade II/VI left parasternal heart murmur and a local cutaneous cuterebral infestation in her dorsal left cervical neck that had subsequently healed. Due to her marked hypernatremia, Lucky was clinically managed with isotonic and hypertonic NaCl infusions to slowly lower her serum sodium concentrations no more than 0.5-1 mEq/L/hr. Clinical diagnostics included routine bloodwork, urinalysis, abdominal ultrasonography, thoracic radiographs, Cryptococcus titers, baseline aldosterone levels, MRI, CSF analysis, FIP PCR, and toxoplasmosis serology. Based on history, physical examination findings, and diagnostics, a presumptive diagnosis of acquired (idiopathic) adipsia was made. This seminar reviews the pathophysiology, causes, clinical management, and prognosis of secondary hypernatremia due to adipsia.