The result of percutaneous superfine-needle aspiration biopsy in 100 patients with intrathoracic lesions guided by simulator is reported. The success rate of aspiration biopsy was 94%, and no major complication was observed. The method of localization by simulator had advantages such as accuracy in localization, no limitation of mass size and site, and a high rate of puncture success. Cell smears obtained by superfine needle were similar to those obtained by fine- or large-bore needles, but fewer complications were encountered. This is a useful technique that can provide early cytological diagnosis, especially for the peripheral type of pulmonary mass.