The safety and activity of obinutuzumab (GA101) plus chemotherapy in relapsed/refractory follicular lymphoma was explored in 56 patients. Participants received obinutuzumab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (G-CHOP; every 3 weeks for 6 to 8 cycles) or obinutuzumab plus fludarabine and cyclophosphamide (G-FC; every 4 weeks for 4 to 6 cycles). Patients were randomly assigned to either obinutuzumab 1600 mg on days 1 and 8 of cycle 1 followed by 800 mg on day 1 of subsequent cycles or 400 mg for all doses. Treatment responders were eligible for obinutuzumab maintenance every 3 months for up to 2 years. Grade 1⁄2 infusion-related reactions (IRRs) were the most common treatment-related adverse event (AE) (all grades: G-CHOP, 68%; G-FC, 82%). Grade 3⁄4 IRRs were rare (7%) and restricted to the first infusion. All patients received the planned obinutuzumab dose. Neutropenia was the most common treatment-related hematologic AE for G-CHOP (43%) and G-FC (50%). At induction end, 96% (27⁄28) of patients receiving G-CHOP (complete response [CR], 39% [11⁄28]) and 93% (26⁄28) receiving G-FC (CR, 50% [14 of 28]) achieved responses. G-CHOP and G-FC had an acceptable safety profile with no new or unexpected AEs, but G-FC was associated with more AEs than G-CHOP. Obinutuzumab plus chemotherapy resulted in 93% to 96% response rates, supporting phase 3 investigation. This trial was registered at www.clinicaltrials.gov as #NCT00825149.