Hyponatremia is a relatively common electrolyte disorder. Although severe acute hyponatremia following coronary angiography is rare, potentially lethal neurologic manifestations may result. We describe a patient with severe, symptomatic hyponatremia, an unusual complication of coronary angiography. Lack of familiarity with contrast media-related hyponatremia caused a delay in diagnosis and therapy in our case. The diagnosis of acute hyponatremia should be considered in any patient who develops behavioral or neurologic manifestations following coronary angiography. Prompt diagnosis and treatment is essential to avoid permanent neurologic damage or death.