Good's syndrome is an infrequent disorder associated with humoral immunodeficiency and thymoma. Patients usually present severe or chronic infections. The most frequent are sinopulmonary infections sometimes associated with bronchiectasias. Another complication is chronic diarrhea, frequently associated with malabsorption, which can be due to a mucosal lesion, infection with gastrointestinal pathogens, or bacterial overgrowth. We describe a patient with Good's syndrome and chronic diarrhea due to bacterial overgrowth.