A case illustrating the infrequent association of sarcoidosis and lymphoma which was also a secretor of a monoclonal IgM paraprotein is described in a 68 year old woman. The first entity manifested by dyspnea corresponded with a bilateral interstitial pneumopathy with restrictive syndrome and was diagnosed by bronchoalveolar lavage and transbronchial biopsy and biopsy prescalenic fat. The lymphoma presented three years later followed by lymphadenopathies and a monoclonal IgM peak being diagnosed by biopsy of an axillary lymph node. In order to relate both entities it has been suggested that prolonged stimulation of the lymphocytes peculiar to the sarcoidosis would cause its malignant transformation.