Objective This study was performed to assess the complication and diagnostic rates of computed tomography (CT)-guided transthoracic needle biopsy of pulmonary parenchymal and mediastinal lesions. Methods Patients who were suspected to have a malignancy based on chest imaging and CT and could not be otherwise diagnosed were evaluated. Results Sixty-five patients were included; 48 (73.8%) were male and 17 (26.2%) were female. Their average age was 58 years. The lesion size ranged from 11 to 105mm. The most common specific histologic subtype was adenocarcinoma, and the least common was lymphoma. The diagnostic rate was 90.8%. The mean complication rate was 15.4%. Statistically significant associations were found between the complication rate and needle size and between the needle path length and lesion size. Conclusion CT-guided needle biopsy is an effective diagnostic method for patients with mediastinal and parenchymal lesions before thoracotomy. This method can also reliably differentiate benign and malignant tumors.