We describe a patient with a 19-year history of lymphocytic lung infiltrations. A diagnosis of lymphocytic interstitial pneumonitis was made in 1982 after an open lung biopsy, but in 1995 a comprehensive re-evaluation led to the diagnosis of Waldenström's macroglobulinaemia with primary bronchopulmonary involvement. It could also be demonstrated by polymerase chain reaction and immunological techniques that this disease had been present since before 1982. In 1995 it was still difficult to demonstrate bone marrow involvement, even with new and sensitive methods. We discuss some diagnostic problems of organ manifestations of uncommon systemic diseases. Pulmonary manifestations of Waldenström's macroglobulinaemia or other diseases of the immune system should be considered in patients with atypical lung disorders.