Vasculitis is definitely associated with familial Mediterranean fever. This familial Mediterranean fever-associated vasculitis takes one of three forms: polyarteritis nodosa, with or without microscopic polyangiitis, and Henoch-Schonlein purpura. Behcet disease and inflammatory bowel diseases may also be associated with familial Mediterranean fever, though this is yet to be formally proven. The selective biological advantage, if any, for carriers of simple heterozygotic mutations in the gene responsible for familial Mediterranean fever, MEFV, is not known. Indirect arguments are given for a better defense against certain groups of bacterial pathogens and amongst intra-cellular bacteria, Mycobacterium tuberculosis.