Parietal pleural invasion of non-small cell lung cancer (NSCLC) is a factor for poor prognosis, and a tumor of any size that invades the parietal pleura is classified as T3. However, with microscopic invasion beyond elastic fibers of the visceral pleura but no penetration to the parietal pleura at tight adhesion sites (we term this p1-3), classification as to the T factor is unclear. Among 1,179 consecutive patients with NSCLCs who underwent curative surgery between 1980 and 2002, 20 were in this category. Here, a comparison was made with subgroups of p stages IB, II, and IIIA with regard to histology, pleural invasion, and survival rates. To maximize the power of assessing prognostic potential, we set the significance level at 0.10, one-sided. The p1-3 condition sites of the 20 cases were the parietal pleura for 17 cases and the pericardium, diaphragm, and chest wall for one each of the remainder. The 5-year survival rate for these p1-3 patients was 71.6%. Significant differences were observed between p1-3 and IIIA groups. Although the 5-year survival rates did not significantly differ between p1-3 and T3N0 or unequivocal T3 subgroups, the prognosis of p1-3 patients was rather better than that of T3 and identical to T2. It was demonstrated that p1-3 status is not a factor warranting T3 classification for NSCLCs. Considering the prognosis, pathologic p1-3 tumors should be managed as a T2 disease for the present.