The incidence, clinical manifestations, morbidity, and mortality of all adult hypernatremic patients hospitalized during a 6-month period were studied. The impact of age on this parameter was evaluated, and the velocity of correction that produced best clinical results was established. Records of all patients who were admitted or developed hypernatremia (Na+ > 150 mEq/L) were reviewed. Demographic characteristics of age, gender, associated diagnosis, length of stay, source of admission, treatment, and outcome were recorded. Of 3209 hospitalizations, 111 patients were hypernatremic (3.46%). Sixty-five were admitted with hypernatremia, and 45 developed hypernatremia while hospitalized. Fifteen had recurrent episodes of hypernatremia. Forty-nine had associated hypokalemia and six had hypercalcemia. The etiology was multifactorial and varied with age. Correction of the hypernatremia within 4 days produced significant improvement in mental status. The overall mortality was 48.6%, and age did not favorably influence mortality. Hypernatremia is a common disorder of elderly hospitalized patients, associated with high mortality and morbidity. Other electrolyte disorders that impair the kidney concentrating ability frequently are observed. The etiology is multiple, and febrile illness due to bacterial infections is the most common cause among the elderly. Prompt treatment of infections and increased water intake in this group of patients could prevent its development. Correction over a 72-hour period significantly improved recovery of mental functions.