Hyponatremia may affect every age group but it has a higher incidence among elderly. An increased prevalence of hyponatremia has been shown in the presence of comorbid condition, although very few studies include uptodate information on the relationship between severity of hyponatremia and comorbidity. The aims of our study are that; comorbid conditions in elderly inpatients diagnosed with hyponatremia and the relationship between hyponatremia severity and comorbid conditions. A total 978 patients aged 65 years and older admitted in hospital were considered for our study. 176 patients with serum sodium < 135 mEg/L were included in the study. Sodium levels between 126-135 mEq/L were defined as mild, between 116-125 mEq/L as moderate and 115 mEq/L and below as severe hyponatremia. The relationships between severity of hyponatremia and comorbid conditions were examined. Patients' mean age was 76.1 +/- 7.2 years (65-95 years). Hyponatremia was significantly higher among women (female/male: 109/67; 61.6%/38.4%). 121 (68.7%) patients had mild, 41 (23.2%) had moderate and 14 (7.9%) had severe hyponatremia. 92 (52.2%) patients had diabetes mellitus, 130 (73.8%) had hypertension and 87 (49.4%) had chronic renal failure. A significant relationship was found between hyponatremia severity and ischemic and congestive heart diseases, neurological disorders, psychiatric disorders and thyroid dysfunction. In addition, mild hyponatremia decreased, moderate and severe hyponatremia increased with higher number of comorbidities. Comorbid conditions may cause hyponatremia through several mechanisms but severity of hyponatremia may differ. Hospitalizations, morbidity, mortality rates and healthcare expenses due to hyponatremia can be reduced with regular care of geriatric patients.