The purpose of this study is to assess the efficacy and safety of mycophenolate mofetil in the treatment of Wegener's granulomatosis and related vasculitides in patients who have contraindications to methotrexate or cyclophosphamide or have experienced disease relapse while on these agents. Mycophenolate mofetil is a novel immunosuppressive agent which has been approved by the FDA for renal transplantation. It is chemically similar to and has a potentially greater efficacy in preventing acute transplant rejection than azathioprine, a drug which has been previously used as an alternative treatment for vasculitis. In this study, patients who have had disease relapse or contraindications to methotrexate will initially receive cyclophosphamide and glucocorticoids and then switch from cyclophosphamide to mycophenolate mofetil upon disease remission. If at the end of two years of mycophenolate mofetil therapy there is continued evidence of disease remission, the drug will be tapered and discontinued. Patients with contraindications to both cyclophosphamide and methotrexate will be treated initially with prednisone and mycophenolate mofetil with mycophenolate mofetil being continued for two full years after disease remission and then tapered and discontinued. For patients who develop intolerance to methotrexate or cyclophosphamide while their disease is in remission, mycophenolate mofetil will be started and continued for two years after which time it will be tapered and discontinued. Patients will be prospectively monitored for evidence of disease activity and drug toxicity. Specific parameters that will be obtained include the time to disease remission, the rate and time of disease relapse, and the incidence of drug related adverse effects.