The clinical spectrum of arthritis in 124 children with well-documented familial Mediterranean fever (FMF) was investigated in a retrospective study. Seven mutations in the FMF gene (MEFV) were also screened using restriction enzyme digestion and amplification refractory mutation system techniques in 110 patients. Mean age at the onset of FMF arthritis was 5.93+/-3.50 years, 75% of the patients being under 10 years of age. Arthritis in the lower extremities, upper extremities, and small joints of the hands and feet was noted in 122 (98%), 17 (14%), and 15 (12%) patients, respectively. Three patients had atypical arthritis involving temporomandibular, sacroiliac, and sternoclavicular joints. Although most of the arthritic attacks resolved within a few weeks, 12 (10%) patients developed protracted arthritis persisting for months. Amyloidosis was demonstrated in 17 (14%) patients who had not received colchicine treatment. Mutation analysis confirmed the diagnosis of FMF in 77 (62%) children. The clinical presentations of arthritis in FMF may be an important source of diagnostic confusion in FMF. Mutation analysis is of value in situations of diagnostic uncertainty.