We present the clinical and histopathological findings of an unusual pulmonary plasmacytoma associated with light chain deposits. The tumour was located in the main left stem bronchus 40 mm from the carina. Histologically, it was composed of sheets of well differentiated plasma cells. Large extracellular deposits of amorphous material were observed in the tumour. These deposits were Congo red negative and contained kappa light chains. They were electron dense granular and non-filamentous. No plasmacytosis was identified by bone marrow biopsy and no monoclonal spike was shown by serum and urine electrophoresis. Our case is unusual in being endobronchial and showing light chain deposition.