The authors investigated the effectiveness of the blood patch technique in reducing the pneumothorax and chest tube insertion rates after transthoracic needle lung biopsy. Biopsy of 100 pulmonary nodules was performed with a coaxial system. In this prospective, randomized study, patients either received a blood patch (group A, n = 46) or did not (group B, n = 47). Seven procedures were excluded: five for technical reasons and two because of lack of follow-up information. Comparison of the two groups by means of X2 analysis and the Student t test revealed no difference in the mean age, gender, smoking history, proportion of heavy smokers, nodule size, presence of cavitation, or number of needle passes. The pneumothorax rate was 24% (11 of 46 patients) in group A and 30% (14 of 47 patients) in group B. The chest tube insertion rate was 2.2% (one patient) in group A and 2.1% (one patient) in group B. The difference between the groups in either rate was not significant (P greater than .5). The blood patch technique did not lower the rate of pneumothorax or chest tube insertion.