Safety data were pooled and analyzed from one phase 2 and two phase 3 double-blind, placebo-controlled, repeat-dose systemic lupus erythematosus (SLE) trials of belimumab 1, 4 (phase 2 only), and 10 mg/kg. Types and rates of adverse events (AEs) were similar across treatment groups. Rates of patients experiencing any serious AE were 16.6%, 19.5%, 13.5%, and 18.0% with placebo, and belimumab 1, 4, and 10 mg/kg, respectively; rates of serious infusion reactions (including hypersensitivity reactions) occurring on the same days as infusions were 0.4%, 0.9%, 0%, and 0.9%, and rates of serious infections were 5.5%, 7.1%, 6.3%, and 5.3%. Malignancy rates/100 patient-years (excluding non-melanoma skin cancer) were 0.29 with placebo vs. 0.20 with all belimumab doses combined; mortality rates/100 patient-years were 0.43 vs. 0.73. These data support the conclusion that belimumab in combination with standard SLE therapy was generally well tolerated in a predominantly autoantibody-positive population with active SLE.