We report the case of a female aged 67 years suffering a Waldenström's macroglobulinemia which began with arthritis at the knee and pleural effusion. In both locations the anatomopathological examination showed infiltration by typical lympho-plasmatic cells. Other possible etiologies such as amyloid, infection or arthritis produced by microcrystals were ruled out. The relevant finding in this case was the presence of infiltrative reaction at the synovial tissue which has been rarely reported in the literature. We review the incidence of articular manifestations in cases of Waldenström's macroglobulinemia and the possible pathogenetic mechanisms involved.