Video-assisted thoracoscopy using a miniaturized endoscope (mini-VAT) was applied for preoperative diagnosis in general thoracic surgery. Thirty-one patients, including 27 with indeterminate pulmonary nodule and 4 with suspected pleural involvement of lung cancer or metastatic pleural tumor, underwent mini-VAT. As a pilot study, 14 of the former 27 patients underwent mini-VAT while receiving general anesthesia. As a prospective study, all the remaining 17 patients underwent mini-VAT while receiving local anesthesia. Solid scopes of three different sizes, 0.9, 1.9, or 4.0 mm diameter, were used. An artificial pneumothorax for scope introduction was produced by needle thoracentesis under atmospheric pressure. Automatic cutting needle biopsy was used for tissue sampling. In the pilot study group, mini-VAT with a 4.0-mm scope provided excellent visibility and diagnostic sensitivity of 100%. This study group showed the diagnostic sensitivity of needle biopsy for pulmonary nodule to be 100%. Hemorrhages and air leaks at biopsy sites were sealed with blood coagulation in a short time. In the prospective study group, mini-VAT with a 4.0-mm scope with the patients receiving local anesthesia provided a diagnostic sensitivity of 91% for pulmonary nodule and a diagnostic accuracy of 100% for suspected pleural involvement. Causes of failure of mini-VAT with the use of local anesthesia were cough reflex during needle biopsy and incomplete lung collapse for deeply located target in two cases. The adverse effects of the mini-VAT were paradoxical respiration in two cases in which local anesthesia was used. The patients who received only local anesthesia required no chest tube drainage. Mini-VAT is a simple, minimally invasive procedure suitable as a preoperative examination technique for histologic diagnosis, evaluation of disease progression, and selection of strategy in thoracic surgery.