Objectives: We investigated the prevalence of Behçet's syndrome (BS) among the ethnic Armenians in Istanbul using Familial Mediterranean Fever (FMF) as a comparator disease. We also studied HLA-B51 and MEFV mutations among a group of healthy Armenians and a non-Armenian population. Methods: The prevalence study was conducted in 2 parts in the Armenian primary schools in Istanbul, using the enrolled students as index cases to study the core family. In Part I, a questionnaire seeking only whether either parent had previously been diagnosed as having BS or FMF by a physician was distributed to a total of 1873 index students registered at 10 schools. A total of 1380 parents filled in the questionnaire, yielding a response rate of 37% (1380 / 3746). In Part II, eight schools participated with a response rate of 83 % (1183/1428). Also, genomic DNA samples of 108 healthy (14 M/ 94 F) Armenians and 97 (45 M/ 52 F) non-Armenians, were studied for HLA-B51 and MEFV gene mutations. Results: In Part I, none of the parents turned out to have been diagnosed as BS, whereas a total of 12 / 1380 (870/105) had been diagnosed as FMF. In the second part the estimated prevalence of BS was 90 /105 and that of FMF was 760/ 105. HLA-B51 carrier rate was found to be similar between the Armenian (27%, 29/108) and the non-Armenian participants (19%, 18/97), (p=0.158). Overall carrier rate of MEFV gene mutations was significantly higher in the Armenian group (36% vs. 20%, p=0.015). Conclusions: The genetic load for FMF is considerably higher among the Armenians when compared to the load for BS among the same ethnic group. On the other hand, the rather low frequency of BS among the Armenians when compared to the frequency among the general population living in the same environment is further evidence for a genetic predisposition to BS. HLA- B51 does not seem to play a dominant role in the said predisposition. Finally, as we have used an unorthodox epidemiological methodology in data collection our results might need to be further verified by more conventional methods. © Copyright Clinical and Experimental Rheumatology 2010.