The possibility that genetic susceptibility to celiac disease (CD) might be influenced by tumor necrosis factor (TNF) genes polymorphism has repeatedly been put forward. To date, this has only been investigated in case-control studies and results have been contradictory. In order to avoid any possible ethnic mismatching between patients and controls, we have approached this problem studying 71 celiac families, establishing the parental haplotypes and comparing CD versus control haplotypes (the so-called AFBAC or affected family-based controls). We used DNA-based methods to screen for HLA-DRB1, -DQA1, and -DQB1 alleles, TNFalpha promoter polymorphims and TNFa and b microsatellites. The guanine-to-adenine polymorphism at position -308 of the TNFalpha gene promoter region was found associated with CD as the TNF-308A allele appeared significantly increased in frequency in CD haplotypes, and this was shown to be independent of the association between CD and the DRB1*0301,DQA1*0501,DQB1*0201 alleles. Our results indicate that at least another gene, in addition to the known association of CD with HLA class II, has a susceptibility role in this disease. This should be either TNFalpha or another polymorphic gene in the telomeric end of the HLA class III region.