Juvenile rheumatoid arthritis (JRA) is a complex disease involving the interactions of several cell populations with different mediators. Herein, we report a five-year-old girl with systemic-onset JRA. At admission, peripheral blood flowcytometric analysis showed the percentages of CD19(+) and CD20(+) B cells were <1%. These values returned to normal on the tenth day of steroid treatment. This is the first report of JRA presented with absence of B lymphocytes in the literature and suggested that lymphocytes subset analysis could change with treatment in patients with JRA. Different clinical signs and symptoms reflecting aspects of JRA are critical for the etiology of the disease and to identify new strategies for treatment.