Hyponatremia is a common epiphenomena amonghospitalized patients. Hyponatremia is commonly associated with high mortality rate in this group. In the review, we discuss the background of hyponatremia with further differential diagnosis and treatment, and highlight the pitfalls in differential diagnosis of hyponatremia. Understanding the cause of hyponatremia can lead to timely and appropriate clinical therapy, which can improve the patient's survival rate.