Background: Hyponatremia is the most frequent electrolyte disorder. However, hyponatremia rarely results from excessive water intake, unless the kidney is unable to excrete free water, such as in patients on thiazide diuretics; in addition, hyponatremia is an uncommon cause of rhabdomyolysis. Methods: We present a 51-year-old hypertensive woman on chronic hydrochlorothiazide therapy who developed acute water intoxication and severe myalgias. Results: The patient developed acute hypotonic hyponatremia and subsequent rhabdomyolysis. We discuss the mechanisms responsible for the development of hyponatremia and its association with rhabdomyolysis. Conclusion: Muscle enzymes should be monitored in patients with acute hyponatremia who develop muscle pain, and hyponatremia-induced rhabdomyolysis must be considered in patients with myalgias receiving thiazide diuretics.