It is known that celiac disease is strongly associated with an HLA class II component and that most patients carry the dimer DQA1*0501, DQB1*0201. We show in this study that the risk for a carrier of this heterodimer is independent from the number of possible heterodimers, from whether DQA1*0501 and DQB1*0201 are in cis or trans position and from the number of DQA1*0501 (one or two) but strongly depends on the number of DQB1*0201. In the Tunisian population we studied, the risk of developing celiac disease is estimated to be 6.8 times greater for those having a double dose of DQB1*0201 than for other dimer carriers. We replicated this result in published data of four other populations (Italy, Czekoslovakia, United Kingdom, Norway).