Diuretics are one of the most common causes of severe hyponatremia. Yet, despite several relevant studies and years of clinical experience, the mechanism and optimal treatment of diuretic-induced hyponatremia remain unclear. What is clear is that most cases are caused by thiazide rather than loop diuretics and that severe hyponatremia can develop very rapidly in susceptible patients. In this review, I will discuss the pathogenesis, clinical features, prevention, and treatment of diuretic-induced hyponatremia in the hope that increased awareness and understanding will reduce the incidence and complications of this potentially life-threatening syndrome.