Syndrome of inappropriate antidiuretic hormone (SIADH) is a disorder of the posterior pituitary gland where vasopressin (ADH) is secreted even when plasma osmolality is normal or low. SIADH, or Schwartz-Barter syndrome, occurs when ADH is secreted in the presence of a low plasma osmolality. This alteration results in increased levels of anti-diuretic hormone. High levels of ADH results in excretion of sodium. The incidence is unknown but might be related to cancers, viral and bacterial pneumonia, lung abscesses, tuberculosis, chronic obstructive pulmonary disease, mycoses, positive pressure ventilators, pneumothorax, brain tumors, head trauma, certain medications, and infectious diseases. Signs and symptoms include nausea, vomiting, muscle twitching, changes in level of consciousness, and low sodium levels with increased urine sodium. The treatment for SIADH includes fluid restrictions because fluid further dilutes the serum sodium levels, gradual replacement of sodium, and administration of demeclocycline (Declomycin) and intravenous hypertonic sodium.