In 3 patients rapidly progressive glomerulonephritis revealed plasma cell dyscrasia in 2 cases and Waldenstrom’s macroglobulinemia in the 3rd. Renal biopsy showed proliferative glomerulonephritis with marked endo- and extracapillary (crescentic) proliferation. In case 1, corticosteroids and cyclophosphamide favorably influenced the course of the disease. The 2nd patient was not treated and went on to maintenance hemodialysis. In the 3rd case, plasma exchange and cytotoxic drugs allowed discontinuation of hemodialysis. Thirteen other cases of proliferative glomerulonephritis associated with monoclonal gammapathies have been described in the literature, including 3 with crescents. B-cell dyscrasia should be considered a possible etiology in a patient with crescentic glomerulonephritis. In such case we show that treatment of the hematologic disorder can be followed by a dramatic improvement of renal functio