Diffuse pulmonary affection in rheumatoid arthritis remains a controversial subject that requires further and more accurate investigation. All patients with rheumatoid arthritis attending a general hospital during a six-year period underwent clinical, radiological, and functional pulmonary evaluation and serological investigation. Twenty-five had an open lung biopsy for microscopic examination and immunofluorescence. The histopathological findings in this group were correlated with the clinical, radiological, functional, and serological altercations and with the clinical course of the rheumatoid process as well. Pulmonary affection in this series was a common finding, showing definite histopathological patterns and particular clinical features.