A study of hyponatremia in adult hospital inpatients over 16 yrs old admitted to the medical department of Al-Diwania teaching\ Hospital from the 1st of June 2006 to 10th of November 2006, showed that (50) out of (720) patients studied had serum sodium concentration below 135 meq/L. Twenty five patients (50%) were on diuretics and 16 patients (32%) had heart failure. The commonest type of hyponatremia was euvolemic hyponatremia (52%) Forty one pts. (82%) had symptoms attributable to the hyponatremia. The aim of the study was to determine the incidence, clinical characteristics, and causes of hyponatremia in medical wards of the Al-Diwaniah teaching Hospital.