This article discusses a case of a 63-year-old male with new-onset proteinuria and monoclonal gammopathy. The patient presented with chronic kidney disease and elevated serum creatinine levels. Various differential diagnoses were considered, including renal involvement by AL-type amyloidosis and light chain proximal tubulopathy. A kidney biopsy revealed the presence of proximal lambda light chain tubulopathy with light chain-storing histiocytes. The patient was subsequently diagnosed with multiple myeloma and started on treatment. This case highlights the diverse range of pathologic lesions associated with renal dysfunction in patients with monoclonal gammopathy and emphasizes the importance of kidney biopsy in the diagnosis of related diseases.