Purpose: To determine the risk factors of pneumothorax and chest tube placement after computed tomography-guided core needle lung biopsy (CT-CNB). Material and methods: Variables that could increase the risk of pneumothorax and chest tube placement were retrospectively analysed in 822 CT-CNBs conducted with 18-gauge non-coaxial CT-CNB in 813 patients (646 men and 167 women; range: 18-90 years; mean: 59.8 years). Predictor variables were age, gender, patient position, severity of pulmonary emphysema, lesion size and localisation, contour characteristics, presence of atelectasis, pleural tag and fissure in the needle-tract, length of the aerated lung parenchyma crossed by the needle, needle entry angle, number of pleural punctures, experience of the operator, and procedure duration. All variables were investigated by ×2 test and logistic regression analysis. Results: The overall incidence of pneumothorax was 15.4% (127/822). Chest tube placement was required for 22.8% (29/127) of pneumothoraxes. The significant independent variables for pneumothorax were lesions smaller than 3 cm (p = 0.009), supine and lateral decubitus position during the procedure (p < 0.001), greater lesion depth (p = 0.001), severity of pulmonary emphysema (p < 0.001), needle path crossing the fissure (p < 0.001), and a path that skips the atelectasis (p < 0.001) or pleural tag (p < 0.001); those for chest tube placement were prone position (p < 0.001), less experienced operator (p = 0.001), severity of pulmonary emphysema (p < 0.001), and greater lesion depth (p = 0.008). Conclusions: The supine and lateral decubitus position, a needle path that crosses the fissure, and a path that skips the atelectasis or a pleural tag are novel predictors for the development of pneumothorax. Key words: computed tomography (CT), CT-guided core needle lung biopsy (CT-CNB), pneumothorax, chest tube, pulmonary lesion.