PURPOSE: To describe the CT findings and charicteristic clinical manifestation of primary malignant pulmonarymesenchymal tumors. MATERIALS AND METHODS: This study involved nine histopathologically proven cases of malignantprimary pulmonary mesenchymal tumors, as follows : MFH(n=2), leiomyosarcoma(n=2), pulmonary blastoma(n=1),neurogenic sarcoma(n=1), rhabdomyosarcoma(n=1), liposarcoma(n=1) and hemangiopericytoma(n=1). Two patients weremale and seven were female; their median age was 45. We retrospectively analyzed tumor size, location,characteristic of the peripheral margin, relationship to airways, and whether there was distal atelectasis orobstructive pneumonitis and lymph node involvement. We also reviewed distant metastasis, tumor growth rate and theinterval between surgery and recurrence, as seen on follow-up CT scans(n=6). RESULTS: Lesions were located at theright upper (n=2), right middle (n=1), right lower (n=1) and left lower lobe (n=2); in three cases, the whole leftlung (left upper + left lower lobe) was involved. CT findings showed that in all cases, the largest diameter ofmasses ranged from 3 to 15 cm; a well-demarcated margin was seen (smooth in eight cases, psiculated in one) andthis was well enhanced(inhomogeneous in six cases, homogeneous in three). In six cases, masses encircled ordisplaced the peritumoral small bronchus, and in five cases, were located in the peripheral lung field. In fourpatients who underwent endobronchoscopy, no endobronchial lesions were present, and in six cases scans initial CTscans showed no lymph-node involvement. In two cases, mass size doubled within one month. On initial diagnosis,distant metastasis was seen in seven cases, and in three, recurrent lesions were detected within postoperative sixmonths. CONCLUSION: If in the differential diagnosis of lung cancer, a mass seen on CT images is well demarcated,large, peripheral, inhomogeneously enhanced, encircles or displaces the peritumoral small bronchus, shows earlydistant metastasis, is high locally invasive, and recurs early with relative sparing of the lymph nodes, thepossibility of primary malignant pulmonary mesenchymal tumor shouldbe considered.