A reset osmostat as a cause of hyponatremia can be found in a variety of clinical settings, including pulmonary and neurologic diseases, as well as in physiologic circumstances such as pregnancy. This teaching case describes a 72-year-old white man with a long-standing history of self-medicating with desmopressin acetate (DDAVP) who presented with profound hyponatremia. On discontinuation of DDAVP treatment, he was found to have a reset osmostat. The mild hyponatremia persisted on follow-up. We theorize that the reset osmostat may have developed secondary to long-standing DDAVP use.