Familial Mediterranean fever (FMF) is a hereditary disease commonly found among Jews, Armenians, Turks and Arabs. Recently, FMF was found in the 'Chuetas', a unique community on the island of Mallorca (Spain). To address the question of their possible Jewish origin, we analysed markers known to be linked to the gene responsible for FMF in Jews (MEFV) in this population. We found that 1/3 of the 16p13.3 chromosomes of the 'Chuetas' FMF patients bore the major ancestral haplotypes (S,S2) and their corresponding M694V and E148Q mutations, displayed by Jews from North Africa. Furthermore, we also detected a novel mutation (L110P) in this community. Yet 2/3 of these patients bore S negative haplotypes and lack the mutations commonly known to cause FMF. These results confirm that at least some of the 'Chuetas' share a common origin with Jews. However, they also provide evidence for the possibility of genetic heterogeneity in this disorder.