Abstract Bone marrow (BM) assessment of minimal residual disease (MRD) is prognostic for survival in multiple myeloma (MM). BM is still hypocellular at month 1 post CAR-T, thus the value of MRD negative (MRDneg) status at this timepoint is unclear. We examined the impact of month 1 BM MRD status in MM patients who received CART at Mayo Clinic between 8/2016 and 6/2021. Among 60 patients, 78% were BM-MRDneg at month 1; and 85% (40/47) of these patients also had decreased to less than normal level of both involved and uninvolved free light chain (FLC