Patients with autoimmune type 1 diabetes mellitus have often, besides immune diabetic markers, also other organ-specific antibodies. In many diabetic patients autoimmune thyroid diseases, i.e. Hashimoto thyroiditis and Grave's disease, with silent clinical course can be diagnosed. Because 50% of children with diabetes and significant titres of thyroid autoantibodies (ATA) develop thyroid problems within 3-4 years, examinations of thyroid antibodies should be performed yearly. In cases of significant antibody titres, thyroid function tests and ultrasound assessment are recommended in order to minimize the risk of undiagnosed hypothyroidism in these patients. Coeliac is an other disease commonly coexisting with type 1 diabetes mellitus and autoimmune thyroid diseases. It is recommended that screening for coeliac disease should be part of the routine investigation for all patients. Potential benefits of treatment coeliac disease is more prevalent in individuals with type 1 diabetes mellitus, and when untreated is associated with a number of medical complications, including poor glycaemic control. Identification of patients with coeliac has been facilitated in recent years by serological screening. Initial normal screening does not exclude coeliac and repeated screening is indicated, a positive IgA antibody test to tTG is a more sensitive parameter than EmA for silent coeliac disease in patients with diabetes. Confirmatory small bowel biopsy, however, remains necessary for diagnosis as some patients with positive antibodies may be without histological changes.