To confirm the safety of transthoracic needle biopsy of the lung (TNB) in the outpatient setting, we reviewed our experience with 106 such procedures over three years. We compared the operating characteristics and morbidity with the 65 similar procedures we were asked to perform on hospitalized patients during the same period. Outpatients did not differ from inpatients in mean age, sex, incidence of clinically apparent COPD, size and location of lesion, or number of needle passes. The operating characteristics of the biopsy were the same for the two groups. Pneumothorax occurred in 29 (27 percent) of 106 outpatient and 26 (40 percent) of 65 inpatient TNBs. Few pneumothoraces not present upon completion of biopsy developed during four hours of observation or later. The requirement for chest tube drainage was similar for both groups, 5.7 and 4.6 percent, respectively. With appropriate caution, TNB can be performed safely on an outpatient basis and the cost of an uncomplicated procedure reduced by 27 percent.