Two cases of multiple myeloma (MM) developed late in the course of chronic lymphocytic leukemia (CLL). An 81-yr-old white female developed, after 6 yr of CLL, IgAk MM with sheets of plasma cells abutting sheets of lymphocytes in the bone marrow, multiple pathologic fractures, and 0.26 g/24 free k light chains in the urine. A 74-yr-old white male developed, after 16 yr of CLL, k light chain MM with 20% plasma cells in the bone marrow, multiple panthologic fractures, and 3.7 g/24 hr free k light chains in the urine. In both cases the CLL had responded well to intermittent low-dose chlorambucil therapy, but the MM failed to respond to cyclic melphalanprednisone therapy. A review of 105 cases of CLL seen at the Geisinger Medical Center failed to turn up any other cases of MM developing during the course of CLL. The suggestion that there is an increased prevalence of MM in CLL is an attractive one because both diseases are B cell neoplasms and because of the increased frequency of asymptomatic monoclonal gammopathies in CLL found by others.