We report on a 67 year old man in whom the chest x-ray revealed marked interstitial opacities in both lungs. The diagnosis of Rheumatoid Arthritis (RA) was established by the presence of five criteria of the American College of Rheumatology for diagnosing RA. High resolution computertomography of the chest confirmed the abnormalities seen in the conventional chest x-ray. A biopsy, taken by open lung surgery, showed the typical pattern of pulmonary involvement in RA and confirmed the association of RA and interstitial lung fibrosis. The histologic examination pointed out lymphocytic infiltration of the bronchies, thickened alveolar walls with lymphoplasmarcellular infiltration and an increase in fibrous connective tissue. A congestive heart failure with severe arrhythmias and an obstructive sleep apnea syndrome (OSAS) were diagnosed in addition. The rhythm disturbances were attributed to the participation of the myocardium in RA and/or by the OSAS. By the treatment with prednisolone, methotrexate, mexiletine and continuous positive airway pressure (CPAP) the rhythm disturbances were alleviated and the patient's condition improved.