QUESTION OF THE STUDY: Synchronous primary lung cancers (SPLCs) may pose a radiologic-pathologic and therapeutic dilemma in according to recent WHO classification. PATIENTS AND METHODS: Two cases of surgically treated SPLCs are reported. RESULTS: In the first case two nodules were detected by Computed Tomography (CT) in the upper right lobe. The patient underwent lobectomy and histological diagnosis was adenocarcinoma and squamous cell carcinoma. The second patient presented at CT one nodule in the upper left lobe and another nodule in the upper right lobe. Sternotomic access was chosen for bilateral removal of the lesions. The diagnosis was sarcomatoid carcinoma and large cell neuroendocrine adenocarcinoma. DISCUSSION: The criteria of Martini and Melamed are inadequate for the diagnosis of SPLCs. The use of TTF-1 (thyroid transcription factor-1) is necessary to establish the diagnosis of SPLC in patients with adenocarcinoma of other sites. Bronchioloalveolar carcinomas must be excluded because of their multicentricity. When histology of two tumors found in the same lobe is identical and histotype is adenocarcinoma, large cell carcinoma or sarcomatoid carcinoma, the diagnosis of SPLCs must be excluded and those lesions must be considered as metastatic disease. The prognosis and treatment of SPLCs are discussed after critical review of the literature.