Until recently, celiac disease and wheat allergy where the only conditions associated with gluten. However, patients who complain of symptoms associated with the ingestion of gluten-containing products have been a growing problem in clinical practice, though they lack diagnostic markers for celiac disease, such as negative celiac serology and normal duodenal biopsies, and negative allergy tests for wheat allergy. Therefore, a new clinical term, non-celiac gluten sensitivity, and classification of gluten-related disorders have been proposed. This classification divides glutenrelated disorders into three categories according to their immunopathogenesis: autoimmune (celiac disease, dermatitis herpetiformis and gluten ataxia), allergic (wheat allergy) and probably immune-mediated (non-celiac gluten sensitivity). Clinical manifestation of non-celiac gluten sensitivity includes various gastrointestinal and extraintestinal symptoms which are very similar to those of celiac disease and wheat allergy making their differential diagnosis challenging. In addition, specific biomarkers for non-celiac gluten sensitivity have not yet been discovered, therefore the diagnosis of this disorder is based on the exclusion of celiac disease and wheat allergy. There is a common correlation between gluten ingestion and onset of symptoms in these disorders, as well as symptom improvement after the exclusion of gluten from diet. Thus, gluten-free diet is a common therapy for all gluten-related disorders. However, an accurate diagnosis is certainly needed before the introduction of gluten-free diet. Progress of these disorders and their severity, as well as complications, are very different, so proper diagnosis is of crucial interest. Furthermore, the introduction of gluten-free diet before making a correct diagnosis can lead to false negative results and, consequently, inaccurate diagnosis.