In the present work, we investigate the possible effect of a CAn microsatellite polymorphism in the nuclear factor kappa B1 (NFKB1) gene on predisposition to celiac disease (CD). Seventy-eight Spanish families with CD were genotyped using a polymerase chain reaction (PCR)-fluorescent method, and the transmission patterns of different CAn alleles were analysed. Furthermore, in order to type the CAn polymorphism more accurately, samples between 126 and 144 bp were cloned and sequenced. A trend of association with the 132-bp allele was found (P = 0.02). This allele was more frequently transmitted to affected sibs, although the results of statistical tests were not significant after correction for multiple comparisons. After sequencing, we found that the 132-, 138- and 142-bp alleles had two As at the end of the CA microsatellite, with the other alleles presenting the described pattern (NCB1 nucleotide U60337) for the microsatellite repeats. These results suggest that the NFKB1 CAn microsatellite does not play a major role in CD susceptibility. In addition, a more detailed molecular characterization of the CA microsatellite is described.