Introduction: The study aimed to identify the etiologies of hyponatremia and to improve its management. Method: A prospective study included patients with serum sodium ≤130 mmol/l. Result: The causes were multifactorial in 58%. The most frequent etiology in 52% was the diuretics in combination with inhibitors of renin-angiotensin-aldosterone system. Urea, creatinine, uric acid, serum osmolality, urinary sodium, SUSPPUP, NT-proBNP and bioimpedance spectroscopy are corresponding significantly with clinical diagnosis. Conclusion: Diuretics plus drugs affecting RAAS was the most common etiology