The objective of the study was to investigate whether immunologic and biochemical events occurring in the course of type 1 diabetes mellitus might play a role in the development of the celiac disease. The study was carried out on 223 children with long-standing diabetes mellitus type 1 (DM1). All the patients had TSH, fT4, fT3, urinary albumin secretion rate, IgA, level of antigliadin antibodies (AGA) IgA and IgG, antitissue transglutaminase IgA antibodies, antiendomysium (EmA) IgA and IgG antibodies and antitireoglobulin antibodies, antithyroid peroxidase antibodies evaluated. Serum TNF-α, IL-6, and IL-10 levels were also measured. The group of children with coincident DM1 and celiac disease and without autoimmune thyroiditis was characterized by significantly higher glycosylated hemoglobin, higher serum TNF-α, IL-6 but lower serum IL-10 in relation to the remaining diabetic patients. A statistically significant positive correlation was observed between IgA-anti-tTG and serum TNF-α (R = 0.28, p = 0.026); between IgG AGA and serum IL-6 (R = 0.31, p = 0.023); and between glycosylated hemoglobin and IgA-anti-tTG (R = 0.21, p = 0.001) and IgA antiendomysium (R = 0.22, p = 0.001). Poor metabolic control, persistent elevated levels of proinflammatory cytokines, and decreased level of antiinflammatory cytokines occurring in the course of type 1 diabetes mellitus might influence the incidence of celiac disease.