Transthoracic needle biopsy (TNB) is usually avoided in the presence of pneumothorax. The authors performed computed tomography (CT)-guided transthoracic core biopsy in the presence of pneumothorax in 13 patients (4.9%) selected from 265 patients who received CT-guided TNB over 4 years. These iatrogenic pneumothoraces were induced by previous ultrasound (US)-guided TNB (n = 5), transbronchial lung biopsy (n = 4), and CT-guided biopsy (n = 4). The time interval between previous thoracic intervention and CT-guided TNB ranged from 0 hours to 9 days after transbronchial lung biopsy (average, 4 days). A diagnostic core biopsy was performed in 12 of the 13 patients. Seven lesions proved to be malignant and five were benign. Failure of CT-guided transthoracic core biopsy occurred in a single patient with a previous US-guided biopsy within 24 hours. This patients demonstrated a progressively enlarging pneumothorax and was treated with air aspiration with CT guidance. A successful second biopsy was performed 7 days later after full expansion of the lung. There were no complications related to the procedures. The authors' experience suggests that CT-guided transthoracic core biopsy using small-bore coaxial technique can be safely performed with high-diagnostic yield in patients with stable iatrogenic pneumothorax.