Hyponatremia is a frequent, yet often unrecognized result of water intoxication caused by psychogenic polydipsia in patients with psychiatric disorders such as schizophrenia and anorexia nervosa. The consequences of hyponatremia may include cerebral edema with tonic-clonic seizures and, in extreme cases, death. In cases of hyponatremia seen in psychiatric practices, the use of psychotropic drugs is often necessary to address both the underlying psychiatric problem and reduce the hyponatremia. Therefore, a patient's clinical condition, the risk of side effects, the possible effect of the medication on hyponatremia and a history of prior medication use should be considered when selecting appropriate psychotropics. The present clinical case details the beneficial effects of olanzapine and fluoxetine in treating a patient with anorexia nervosa and body dysmorphic disorder experiencing acute hyponatremia, and the stable effect the medications achieved over a period of 2.5 years of maintenance therapy.