Four cases of familial Mediterranean fever have been reported in which the disease produced organic damage to a joint. The diagnosis was confirmed by clinical and family history and a typical course which included attacks of recurrent joint synovitis. The laboratory findings, while typical, were not specific. The main involvement was in the lower limbs. The findings at operation were of a non-specific synovitis with destruction of cartilage. It is emphasized that in the majority of cases of familial Mediterranean fever the joint involvement is transient and only uncommonly does damage to the joint become permanent. The fact that organic joint damage occurs is not widely recognized, which is the reason for our report of these four cases.