Multiple myeloma (MM) may manifest as diffuse bony disease (myelmatosis), as a solitary plasmacytoma of bone, or as extramedullary (extraosseous) plasmacytoma (EMP). The most frequent thoracic involvement by MM is bone involvement or pulmonary infiltrate secondary to an infectious process. Because MM, which is a disorder of the aged population, with its severe clinical course and heterogeneous symptoms, the diagnosis is difficult. The aim of this study was to investigate the causes, the frequency and the effects of prognosis of the pulmonary involvement in 38 patients with this disorder who were treated between January 1995 and April 2001 at the Department of Chest and Haematology-Oncology at Erciyes University Medical School. The patients with MM; 25 (66%) was male and 13 (34%) was female, and their mean age was 61 +/- 11 range 40-80 years. Of the 38 patients; 19 (50%) had thoracal involvement which included pulmonary involvement in 13 (%35) and thoracal bone invasion in 9 (24%). According to their clinical and radiological findings, the 13 cases with pulmonary involvement were evaluated and six had pneumonia, two had mass lesion, two had multiple nodular lesion, three had intersitial infiltration. Five (13%) of the patients with respiratory symptoms were admitted to the Chest Clinic. Malign plasma cell infiltration was detected by transthoracal lung biopsy in two patients with mass lesions, and with transbronchial lung biopsy in one patient with intersitial infiltration. The cases with pulmonary involvement were associated with progressive diseases, which included mainly renal failure and pathological bone fractures. Pulmonary involvement of MM is frequently associated with rapid progression of the disease and demonstrates the variability of roentgenographic manifestations. MM should be taken into consideration in the differential diagnosis of pulmonary infiltration in older patients with systemic complaints.