BACKGROUND: The association between type 1 diabetes and immunoglobulin A deficiency (IgA-D) has long been recognized in many populations. The aim of this study was to assess the prevalence of IgA-D in patients with type 1 diabetes mellitus all coming from a defined geographical area and to investigate the clinical features of these subjects. METHODS: The records of 150 consecutive patients with type 1 diabetes mellitus referred in a period of one year were analyzed. A detailed history was obtained for each patient. Information was collected concerning age, gender, time of onset of diabetes, and presence of other autoimmune diseases. RESULTS: Out of 150 patients with type 1 diabetes, eight (5.3%) had a diagnosis of IgA-D. There were one female and seven male; all these patients were diagnosed by screening: none of them had history of recurrent infections. Autoimmune thyroiditis was coexisting in five patients (62%). Although other associated autoimmune disorders were found in a number of patients, there was no different prevalence rate in IgA deficient patients. CONCLUSION: This study shows the prevalence of IgA-D in Sicilian patients with type 1 diabetes as 5.3% which is much higher than reported in other Italian studies. Moreover, our data show a high prevalence of IgA-D in male gender and describe thyroiditis as the most frequent autoimmune disease present in these patients. Finally, in our case report, IgA-D diagnosis always followed routine IgA measurement when case finding for celiac disease with no history of recurrent infections in each patient.