We have analyzed the distribution of the major histocompatibility complex (MHC) class I chain-related gene A (MICA) transmembrane alleles among 58 Spanish patients with Behçet's disease (BD) and in 194 ethnically matched healthy controls. The study included the characterization of A4, A5, A5.1, A6 "new" and "old" and A9 MICA-TM alleles using polymerase chain reaction. As previously reported, the serological B51 specificity was increased among this BD patient group (36.25% vs. 19.6% in controls; P=0.009; OR=2.33). The MICA-TM alleles A6 ("new" and "old"), in linkage disequilibrium with HLA-B51 and HLA-B14 respectively, were only slightly increased among patients (70.7% vs. 61.3% in controls; P=NS). We conclude that, in contrast to previous finding reporting a strong association of MICA-TM genes and Behçet disease in Japanese patients, in our population HLA-B51 is more closely associated to Behçet susceptibility than MICA-TM genes. Finally, our data show that in Spain, as occurs in other populations, some MICA-TM alleles exhibit strong linkage disequilibrium with certain alleles of the HLA-B locus.