Specimens of synovial tissues from 5 affected joints of 3 patients with Behçet's disease were available for histopathological examination. All specimens were infiltrated by lymphocytes and neutrophils, and exhibited marked vascularity and infiltration of lymphoid cells among the vessels. Marked plasma cell infiltration and lymphoid follicle formation were found in one synovial tissue sample. There was no evidence of infection or vasculitis. These findings suggest that the histopathological characteristics of synovial tissue in Behçet's disease may have a wide range, some of which may even resemble the synovial tissue of rheumatoid arthritis.