Celiac disease (CD) is a T-cell-mediated enteropathy, triggered in genetically susceptible individuals by the ingestion of wheat gluten or related rye and barley proteins, whose clinical picture disease is considerably heterologous. Patients with CD are at high risk of autoimmune disorders; similarly, CD is frequent in patients with type 1 diabetes mellitus (T1DM), a disorder characterized by the immune-mediated beta-cell destruction, with the cooperation of environmental factors in genetically susceptible individuals. The immunological markers of beta-cell destruction are the autoantibodies to insulin, glutamic acid decarboxylase, and the protein tyrosine phosphatase. In absence of these markers, incidental hyperglycemia in children and adolescents appears unlikely to be associated with the progression to T1DM. We report a girl with CD and incidental hyperglycemia, without immunological markers of T1DM, with a family history for hyperglycemia, and diagnosed as maturity-onset diabetes of the young. We present this case as evidence that the possibility of monogenic forms of diabetes must be suspected in children with incidental hyperglycemia, a family history for mild hyperglycemia or diabetes, and absence of markers of beta-cell destruction, even if the patients are affected by an autoimmune disease.