A case of a 56-years old male with rheumatoid arthritis and unclear tumoral radiological changes in the lungs was described. Since noninvasive diagnostic procedures failed to explain nature of the pulmonary changes, an open pulmonary biopsy was performed. Pathological examination revealed presence of rheumatoid nodules and pneumoconiosis, typical for Caplan's syndrome. In the past, the patient had been working in foundry industry for 16 years and he had been exposed to silica and iron dust. Articular symptoms were revealed prior to finding the lung changes even dust exposure had occurred many years earlier. In spite of the fact that rheumatoid arthritis is a relatively common disease and pneumoconiosis is also not rare entity, the coexistence of both conditions i.e. Caplan's syndrome has been rarely diagnosed and described.