Abstract Background and Aims Renal biopsy is not necessary to assess LCCN (Light Chain Cast Nephropathy) in patients with laboratory features suggestive of the disease. However, it has been shown that the histological picture often correlates with renal outcome. We present the case of a 55-year-old man with no significant previous medical history that was evaluated in the emergency department for a stage 3 AKI (sCr 17.3 mg/dl, eGFR 3 ml/min/1.73 m2). Laboratory tests showed a Lambda Micromolecular Myeloma (K chains 44.6 mg/l, λ 4160 mg/l and K/ λ 0.01); Bence Jones not evaluable due to anuria. Bone marrow plasmacytosis was 70%. Method The patient started chemotherapy with Bortezomib and Dexamethasone and hemodialysis thrice a week with a PMMA hemofilter in order to improve the FLC (Free Light Chain) removal rate. After three months of treatment the patient achieved a complete hematologic response but he didn't reach any renal response. In order to assess a more precise renal prognosis a kidney biopsy was performed. The histopathological exam showed a Cast Nephropathy (< 5 casts/mm2) associated with low grade interstitial fibrosis and tubular atrophy (IFTA +1). After 5 cycles with Bortezomib and Dexamethasone, one year after onset, the patient underwent ASCT (Autologous Stem Cell Transplantation). Results In the following months, a progressive increase in renal function allowed us to perform a gradual reduction of dialysis rate, until discontinuation occurred 16 months after disease onset. To date, three years after onset, complete hematologic and renal remission persists with an eGFR of 20 ml/min/1.73 m2. Conclusion Renal biopsy, performed even several months after disease onset, could play a pivotal role in cases of LCCN with a discordance between hematologic and renal response. A low cast number and low IFTA grade are known to be positive prognostic factors for renal outcome and they can predict a renal recovery that sometimes could be exceptionally late.