This study retrospectively investigated the efficacy and adverse events of applying a lower dose (0.5 g/m(2)) of monthly intravenous (IV) cyclophosphamide (CYC) for lupus nephritis in Korean patients. Adverse events occurred in 64 patients (61.5%) of 104 lupus nephritis patients who were treated with IV CYC, with the most common being those related to the gastrointestinal system, followed by infection, symptoms related to the hematopoietic system, skin and its appendages, reproductive system, and urinary system. Lower-dose IV CYC therapy resulted in renal remission or response in 76 patients (73.1%), which was as effective as the reported outcomes of higher-dose (0.75-1.0 g/m(2)) IV CYC regimens. Adverse events were more likely (with borderline statistical significance, p = 0.055) in those who achieved renal remission or response than in nonresponders.