From 1980 to 1990, 1505 patients underwent thoracotomy as definitive treatment for non small cell lung cancer. Computed tomography (CT) of the chest has been used routinely since 1984 for assessment of mediastinal lymph node involvement. A total of 235 cervical mediastinoscopies and 71 anterior parasternal mediastinotomies were performed on the same patient population as preoperative staging when CT scan demonstrated mediastinal lymph nodes larger than 1 cm. Radical resections showed a constant increase in number from 70.1% in the period 1980-84 to 82.7% in the period 1985-90. Exploratory thoracotomies and thoracotomies with residual tumor showed a parallel reduction: 14.5% in 1980-84 to 7.4% in 1985-90 for the former, 15.4% in 1980-84 to 9.8% in 1985-90 for the latter. The percentage of N2 disease to the total number of thoracotomies decreased from 23.6% in 1980-81 to 11.2% in 1989-90. We conclude that a selective use of cervical mediastinoscopy and anterior parasternal mediastinotomy, based upon the results of CT scan, may have contributed to reduce the number of exploratory thoracotomies and thoracotomies with residual tumor.