Familial Mediterranean fever (FMF) is an autosomal recessive disorder characterized by recurrent and self-limited fever attacks and serositis/arthritis. The M694V, M694I, M680I, V726A, and E148Q mutations in MEFV, the gene responsible for FMF, account for most FMF cases in Mediterranean populations. In Japan, M694I and E148Q are most frequently detected; M694V, M680I, and V726A have not been identified so far. We report the first case of FMF associated with M680I in Japan.