We hypothesize that mycophenolate mofetil(Cellcept)is safe and effective for lupus arthritis. In this study, patients with lupus will be randomly assigned to receive mycophenolate mofetil or placebo (inert pills) for three months. At the end of three months all patients will receive mycophenolate mofetil for three additional months. The effectiveness on arthritis and other symptoms of lupus will be measured by joint counts and by the BILAG instrument (a measure of overall lupus disease activity. Additionally special blood tests aimed at understanding the biologic effects of mycophenolate mofetil will also be performed at some visits. The primary outcome measurement will be the safety and effectiveness of this treatment (as compared to placebo) at the three month point. The trial will continue in a blinded fashion (neither the investigator or the participants know who is getting mycophenolate and who is getting placebo) until 24 patients have completed the first three months of the protocol.