We describe a woman with lymphoid interstitial pneumonia diagnosed by open lung biopsy following a profile of unproductive cough, weakness and bilateral lung infiltrates. The patient was also diagnosed as having common variable immunodeficiency based on hypogammaglobulinemia, repeated sinusitis and persistent diarrhea. Exfoliative cytology of pleural effusion revealed the development of non-Hodgkin's lymphoma. We review the associations among these processes and consider the suggestion made by other authors that lymphoid interstitial pneumonia be considered a prelymphomatous process.