A 74-year-old man presented with mental obtundation and massive ascites without evidence of significant impairment of liver function. Thyroid function studies suggested hypothyroidism. Aspirated ascitic fluid had the characteristics of an exudate. Thyroid replacement therapy resulted in rapid clinical improvement with resolution of the ascites. Prompt recognition of myxedema ascites may prevent the inappropriate use of diuretic agents, therapeutic paracentesis, and sometimes unnecessary laparotomy.