As many as one in every 100 to 200 persons in the United States has celiac disease, a condition resulting from an inappropriate immune response to the dietary protein gluten. The manifestations of celiac disease range from no symptoms to overt malabsorption with involvement of multiple organ systems and an increased risk of some malignancies. When celiac disease is suspected, initial testing for serum immunoglobulin A (IgA) tissue transglutaminase (tTG) antibodies is useful because it offers adequate sensitivity and specificity at a reasonable cost. A positive IgA tTG result should prompt small bowel biopsy with at least four tissue samples to confirm the diagnosis. However, 3 percent of patients with celiac disease have IgA deficiency. Therefore, if the serum IgA tTG result is negative but clinical suspicion for the disease is high, a serum total IgA level may be considered. Screening of asymptomatic patients is not recommended. The basis of treatment for celiac disease is adherence to a gluten-free diet, which may eliminate symptoms within a few months. Patients should also be evaluated for osteoporosis, thyroid dysfunction, and deficiencies in folic acid, vitamin B12, fat-soluble vitamins, and iron, and treated appropriately. Serum IgA tTG levels typically decrease as patients maintain a gluten-free diet.