The chromosomal location of the NFkappaB1 gene on 4q, a region linked to type 1 diabetes (T1D), together with the observed resistance to T1D of NFkappaB1-deficient mice, suggests its potential role as candidate gene increasing diabetes predisposition. Previous association studies in diverse populations yielded inconclusive results. Two polymorphisms in the promoter region of the NFkappaB1 gene have been studied: a functional -94ins/delATTG regulating the gene expression and a very informative CA-repeat microsatellite. A strong association with the latter was reported in British population but could not be replicated in Danish families. No evidence of association was detected for those genetic markers in 270 Spanish T1D patients and 484 healthy ethnically matched controls. Therefore, it seems that this gene plays no major role in T1D predisposition.