Key Words IgE-mediated allergy Skin-prick test Type 1 diabetes Abstract Background: Autoimmune disorders are considered to be associated with a Th1 immune response while allergic diseases with a Th2 response. We carried out a study to determine whether there is an inverse relationship between allergic diseases in IgE-sensitized children or positive skin-prick test reactions to allergens and type 1 diabetes mellitus (DM1) in children. Methods: Sixtythree children with DM1 and 108 controls were enrolled. Parents of all children compiled a questionnaire on allergic diseases. All children underwent skin-prick tests for common aero-allergens and food-allergens. Results: A history of allergic symptoms, especially wheezing, asthma and allergic rhinitis was significantly less common in the group with DM1. Allergic symptoms in children with IgE sensitization or parental atopy were no more likely in children with DM1 than in normal control subjects. There was no association between skin-prick test results to inhalants and food allergens and DM1. Conclusions: Consistently with the Th1/Th2 paradigm, we observed a reduction in the frequency of allergic symptoms in children with DM1. However, our study did not succeed in demonstrating an inverse relation between Th1- and Th2-mediated diseases in children with IgE sensitization or an atopic genetic predisposition. Copyright © 2004 S. Karger AG, Basel Introduction On the basis of the pattern of cytokine production, functional subsets of the T helper cell clones, called Th1 and Th2, have been reported . Allergic diseases , such as asthma, eczema and hay fever, are chronic inflammatory diseases frequently observed in children. Asthma and atopy are thought to be associated with a Th2 cytokine profile which induces an allergen-specific IgE-mediated inflammation [3–5]. On the contrary, autoimmune disorders, such as type 1 insulin-dependent diabetes mellitus (DM1), are characterized by a Th1 phenotype . The Th1 and Th2 response controls the development of the same subset and suppresses the effector cells of the other subset. Therefore, it has been suggested that allergic diseases and DM1 are mutually exclusive and unlikely to be present in the same individual.