From a review of 17 cases of Fanconi syndrome with Bence Jones proteinuria and myeloma or amyloidosis, including three new cases reported here in detail, there emerges a well defined set of characteristics. In most cases, the diagnosis of Fanconi syndrome preceded the development of myeloma or amyloidosis. Myeloma preceding the development of Fanconi syndrome has not been reported. All the patients had Bence Jones proteinuria, but in some it could be detected only by electrophoresis or immunoelectrophoresis, In the seven cases in which the Bence Jones protein was typed, it was of kappa type. There were no serum protein monoclonal abnormalities. In the bone marrow and renal samples of half of the patients, crystalline cytoplasmic inclusion bodies were present in lymphoplasmacytic elements and renal tubular cells. It is proposed that patients with Fanconi syndrome and Bence Jones proteinuria have a distinct type of plasma cell disorder or variant of the monoclonal gammopathies, characterized by a slow progression of the tumor and by an early phase dominated by the metabolic complications of the renal proximal tubular dysfunction. Adult patients with Fanconi syndrome should be carefully investigated for the presence of Bence Jones protein and a plasmacytic dyscrasia should be excluded.