The spectrum of renal lesions associated with deposition of monoclonal light chains is varied and extensive, yet the simultaneous occurrence of two or more of these lesions in the same patient is unusually recognized. In addition, patients may excrete large amounts of monoclonal light chains and have no clinically evident renal dysfunction. Thus, the type of renal lesion that occurs appears to depend on the physiochemical properties of the unique monoclonal light chain produced. The particular nephrotoxic properties responsible have not yet been identified but are currently under intensive examination. For example, various studies suggest that cast-forming Bence Jones proteins have isoelectric points above 5.1. Finally, along with these intrinsic properties, environmental factors combine to promulgate the lesion or prevent clinical expression of renal injury. Attention to the subtle morphological renal manifestations of MLCRRD is essential to diagnose these diseases early in the course. Characterization of the morphological pattern and degree of renal affectation is important because therapeutic modalities may vary accordingly. As understanding of the molecular events responsible for the renal alterations improves, additional therapeutic approaches may emerge to reverse renal failure in MLCRRD.