Several studies indicate genetic involvement of Th2 cytokines in allergic diseases. Interleukin (IL)-13 has been mapped to the cytokine cluster on chromosome 5q31–33, which has been associated with atopic conditions. Recently, an association was reported between the T allele in a promoter polymorphism in the IL-13 gene (C to T exchange) at position −1055 and allergic asthma in a population study in the Netherlands. This observation was apparently confirmed in a case–control study using probands and spouses from a Dutch asthma family study, but the polymorphism in that study was reported to occur at position −1111. In the present study, we established that this polymorphism is located at position −1024 relative to the ATG translation initiation codon, and investigated whether it confers a genetic predisposition to atopic conditions and the Th1 condition multiple sclerosis (MS) in Caucasian subjects. We confirmed the association between the IL-13 −1024TT genoype and inhalation allergy (P = 2.4E-02). By combining the data from the three studies, we demonstrated a strong association (P = 1.09E-05) between the IL-13 −1024 marker and inhalation allergy. Furthermore, we showed for the first time that this association also exists in atopic dermatitis (P = 2.0E-02). No association with MS was found.