Carfilzomib (CFZ) is a non-reversible proteasome inhibitor approved for the treatment of patients with relapsed and refractory myeloma (RRMM). Its use has been associated with cardiovascular toxicity but although recently a signal of clinically significant renal complications has also been identified, it is less extensively investigated. We analyzed data of 114 consecutive patients with RRMM who received CFZ-based regimens. Renal complications not related to MM progression were observed in 19 (17%) patients; thrombotic microangiopathy (TMA) was seen in 6 (5%) patients, albuminuria >1 gr/day in 7 patients (6%) and at least grade 3 acute kidney injury (AKI) which could not be otherwise explained in 6 patients (5%). A total of 15 patients discontinued CFZ and dosing was reinitiated at a lower level in one patient with AKI. Albuminuria was associated with focal segmental glomerulosclerosis in the renal biopsy (performed in a total of 6 patients). Renal complications during CFZ therapy are common, occur mostly early and are unpredictable. A potential effect of CFZ on the renal endothelium could be implicated in the pathogenesis of these complications and may also share common pathophysiology with cardiovascular effects of CFZ.