A 77-year-old man with a history of cardiac transplantation and pulmonary tuberculosis was admitted for initiation of chemotherapy for multiple myeloma. His kidney function had worsened over several months, which was attributed to multiple myeloma–related kidney disease. Large bilateral kidney cysts precluded biopsy. Upon admission, he was found to have elevated gamma fraction and high IgG κ light chain levels. A peripheral smear showed over 20% plasma cells, diagnostic of progression from multiple myeloma to plasma cell leukemia.