The variable number of tandem repeats polymorphic region upstream the insulin gene on chromosome 11p15.5 (IDDM2) has been linked to type I (insulin-dependent) diabetes mellitus sus- ceptibility and, in several populations, class I alleles have been associated with increased risk to the disease while class III alleles are dominantly protective. PCR-based methods for class I subtyping have shown allelic heterogeneity concerning their contribution to diabetes risk. The aim of the pre- sent work was to analyse the IDDM2 locus in the Spanish population. We observe that among Spa- niards, the class I/I homozygous genotype is associated with a two-fold increased risk for type I diabetes, which is lower than that observed among other populations, and could be explained by the high prevalence of non-predisposing class I alleles in the general population from Spain.