To define a possible association between familial Mediterranean fever (FMF) and seronegative spondyloarthropathy (SNSA) and to study features of SNSA in FMF patients, we screened for the presence and manifestations of SNSA in 3,000 FMF patients attending the National Center for FMF in our institution. This population included 160 patients with chronic arthritis, most who suffered from SNSA. Patients were considered to suffer from SNSA if they had chronic arthritis, inflammatory back/neck pain, and sacroiliitis. Patients who had other diseases associated with SNSA were excluded. Eleven patients, nine men and two women, with chronic monoarthritis or oligoarthritis, grade 2 (four patients) or grades 3 to 4 (seven patients), sacroiliitis, and inflammatory back pain met the criteria for diagnosis of SNSA of FMF. These patients were rheumatoid factor (RF) and HLA-B27 negative. In seven patients, spondyloarthropathy developed while they received colchicine, and in four before colchicine. Most patients responded to treatment with nonsteroidal antiinflammatory drugs, but three required second-line agents. These findings suggest that SNSA is one of the musculoskeletal manifestations of FMF that may occur despite colchicine therapy and requires specific treatment.