Hyponatremia can complicate thiazide use in a minority of susceptible individuals and can result in significant morbidity and even mortality. Risk factors for thiazide-associated hyponatremia include age, female sex, and possibly low body mass. A genetic susceptibility has recently been uncovered. Although frequently developing early after thiazide treatment initiation, many cases of hyponatremia present after months or years of use. Many cases are asymptomatic or have mild symptoms, but seizures and/or coma may develop, especially in those with acute onset.