The case of a 52-year-old woman with a past history of thymoma resection who presented with chronic diarrhea and generalized edema is the focal point of this article. A diagnosis of Giardia lamblia infection was established, which was complicated by protein-losing enteropathy and severely low serum protein level in a patient with no urinary protein loss and normal liver function. After anti-helmintic treatment, there was recovery from hypoalbuminemia, though immunoglobulins persisted at low serum levels leading to the hypothesis of an immune system disorder. Good's syndrome is a rare cause of immunodeficiency characterized by the association of hypogammaglobulinemia and thymoma. This primary immune disorder may be complicated by severe infectious diarrhea secondary to disabled humoral and cellular immune response. This is the first description in the literature of an adult patient with an immunodeficiency syndrome who presented with protein-losing enteropathy secondary to giardiasis.182430-3