Introduction: Less than 4% of patients with hypothyroidism develop ascites. Ascites as the only presenting feature of hypothyroidism is uncommon, hence diagnosis is often delayed. Once it is diagnosed, treatment of hypothyroidism leads to quick clinical improvement in ascites. We report a case of ascites secondary to severe hypothyroidism.Figure 1Case: A 56 year old female with long standing history of Hashimoto's thyroiditis and non-compliance to thyroid supplementation presented with a four week history of progressive painless abdominal distension. She had recently undergone extensive work-up at a regional hospital. Review of records revealed high ascitic fluid protein content (3.9 g/dl) and serum-ascites-albumin gradient (SAAG) of 1. Ultrasound and computed tomography of the abdomen and pelvis showed massive ascites. Morphology of liver and spleen was unremarkable without any evidence of increased portal pressure. Viral hepatitis serology was negative and tumor markers (CA19-9, CA125) were within normal limits. Hepatic Doppler ultrasound showed normal portal pressure without evidence of portal or hepatic vein thrombosis. We ordered thyroid stimulating hormone level that resulted as >100 units/ml, with low free T4 (0.2 ng/dl). Further evaluation revealed dyslipidemia and mildly elevated alanine and aspartate transaminases and creatine kinase, consistent with thyroid myopathy. The diagnosis of myxedema ascites was made on this diagnostic work-up and the patient was started on thyroid replacement. On a follow-up visit at 4 weeks, there was no clinical evidence of ascites and TSH decreased to 56 units/ml. Discussion: Severe uncontrolled hypothyroidism is a rare but reversible cause of ascites. Various theories have been hypothesized to explain the pathophysiology. These include: 1) an increase in capillary permeability leading to the extravasation of plasma proteins into the extravascular compartment; 2) direct hygroscopic effect caused by hyaluronic acid accumulating in the skin and producing edema; 3) diminished free water clearance due to excess ADH production. Myxedema ascites responds well to thyroid replacement therapy and is completely reversible. Conclusion: Our case illustrates that the diagnosis of myxedema ascites should be borne in mind in a patient with uncontrolled hypothyroidism who presents with ascites. It also signifies the need for testing TSH level as part of the workup for ascites of unknown etiology.