The purpose of this study was to determine the diagnostic accuracy and frequency of complications of CT-guided transthoracic needle biopsy done with an automated biopsy system.Thirty-three consecutive biopsies were performed on 32 patients between February 1992 and July 1994 (mean age, 55 +/- 15 years; 18 men and 14 women). An 18-gauge (n = 28) or 20-gauge (n = 5) needle was used. Core specimens were submitted for pathologic examination in 10% formalin. No cytopathologist or frozen section analysis was available at the time of biopsy. All biopsies but one were performed by one chest radiologist.Thirty-one lung biopsies and two mediastinal biopsies yielded a mean lesion size of 4.0 cm (range, 1.2-13.0 cm). Postbiopsy pneumothorax occurred in three (9%) of 33 biopsies; none of the pneumothoraces required placement of a chest tube. The mean number of needle passes was 1.3 (+/- 0.6). Thirty biopsies (91%) yielded sufficient tissue for pathologic evaluation. The diagnoses included carcinoma in 14 cases, acute ...